diff --git a/packages/localize/src/tools/src/translate/asset_files/asset_translation_handler.ts b/packages/localize/src/tools/src/translate/asset_files/asset_translation_handler.ts
index aea057bff10ad..ed552d0514197 100644
--- a/packages/localize/src/tools/src/translate/asset_files/asset_translation_handler.ts
+++ b/packages/localize/src/tools/src/translate/asset_files/asset_translation_handler.ts
@@ -10,8 +10,6 @@ import {FileUtils} from '../../file_utils';
 import {OutputPathFn} from '../output_path';
 import {TranslationBundle, TranslationHandler} from '../translator';
 
-
-
 /**
  * Translate an asset file by simply copying it to the appropriate translation output paths.
  */
diff --git a/packages/localize/src/tools/src/translate/main.ts b/packages/localize/src/tools/src/translate/main.ts
index 209426c2d93bd..3d3b9e92dc90d 100644
--- a/packages/localize/src/tools/src/translate/main.ts
+++ b/packages/localize/src/tools/src/translate/main.ts
@@ -14,7 +14,7 @@ import {AssetTranslationHandler} from './asset_files/asset_translation_handler';
 import {getOutputPathFn, OutputPathFn} from './output_path';
 import {SourceFileTranslationHandler} from './source_files/source_file_translation_handler';
 import {MissingTranslationStrategy} from './source_files/source_file_utils';
-import {TranslationLoader} from './translation_files/translation_file_loader';
+import {TranslationLoader} from './translation_files/translation_loader';
 import {SimpleJsonTranslationParser} from './translation_files/translation_parsers/simple_json/simple_json_translation_parser';
 import {Xliff1TranslationParser} from './translation_files/translation_parsers/xliff1/xliff1_translation_parser';
 import {Xliff2TranslationParser} from './translation_files/translation_parsers/xliff2/xliff2_translation_parser';
@@ -50,18 +50,21 @@ if (require.main === module) {
             describe:
                 'A glob pattern indicating what translation files to load, either absolute or relative to the current working directory. E.g. `my_proj/src/locale/messages.*.xlf.',
           })
+
           .option('o', {
             alias: 'outputPath',
             required: true,
             describe:
                 'A output path pattern to where the translated files will be written. The marker `{{LOCALE}}` will be replaced with the target locale. E.g. `dist/{{LOCALE}}`.'
           })
+
           .option('m', {
             alias: 'missingTranslation',
             describe: 'How to handle missing translations.',
             choices: ['error', 'warning', 'ignore'],
             default: 'warning',
           })
+
           .help()
           .parse(args);
 
@@ -73,32 +76,67 @@ if (require.main === module) {
   const diagnostics = new Diagnostics();
   const missingTranslation: MissingTranslationStrategy = options['m'];
   const sourceLocale: string|undefined = options['l'];
+  // For CLI we do not have a way to specify the locale of the translation files
+  // It must be extracted from the file itself.
+  const translationFileLocales: string[] = [];
 
-  translateFiles({sourceRootPath, sourceFilePaths, translationFilePaths, outputPathFn, diagnostics,
-                  missingTranslation, sourceLocale});
+  translateFiles({sourceRootPath, sourceFilePaths, translationFilePaths, translationFileLocales,
+                  outputPathFn, diagnostics, missingTranslation, sourceLocale});
 
   diagnostics.messages.forEach(m => console.warn(`${m.type}: ${m.message}`));
   process.exit(diagnostics.hasErrors ? 1 : 0);
 }
 
 export interface TranslateFilesOptions {
+  /**
+   * The root path of the files to translate, either absolute or relative to the current working
+   * directory. E.g. `dist/en`
+   */
   sourceRootPath: string;
+  /**
+   * The files to translate, relative to the `root` path.
+   */
   sourceFilePaths: string[];
+  /**
+   * An array of paths to the translation files to load, either absolute or relative to the current
+   * working directory.
+   */
   translationFilePaths: string[];
+  /**
+   * A collection of the target locales for the translation files.
+   */
+  translationFileLocales: (string|undefined)[];
+  /**
+   * A function that computes the output path of where the translated files will be written.
+   * The marker `{{LOCALE}}` will be replaced with the target locale. E.g. `dist/{{LOCALE}}`.
+   */
   outputPathFn: OutputPathFn;
+  /**
+   * An object that will receive any diagnostics messages due to the processing.
+   */
   diagnostics: Diagnostics;
+  /**
+   * How to handle missing translations.
+   */
   missingTranslation: MissingTranslationStrategy;
+  /**
+   * The locale of the source files.
+   * If this is provided then a copy of the application will be created with no translation but just
+   * the `$localize` calls stripped out.
+   */
   sourceLocale?: string;
 }
 
-export function translateFiles({sourceRootPath, sourceFilePaths, translationFilePaths, outputPathFn,
-                                diagnostics, missingTranslation,
-                                sourceLocale}: TranslateFilesOptions) {
-  const translationLoader = new TranslationLoader([
-    new Xliff2TranslationParser(),
-    new Xliff1TranslationParser(),
-    new SimpleJsonTranslationParser(),
-  ]);
+export function translateFiles({sourceRootPath, sourceFilePaths, translationFilePaths,
+                                translationFileLocales, outputPathFn, diagnostics,
+                                missingTranslation, sourceLocale}: TranslateFilesOptions) {
+  const translationLoader = new TranslationLoader(
+      [
+        new Xliff2TranslationParser(),
+        new Xliff1TranslationParser(),
+        new SimpleJsonTranslationParser(),
+      ],
+      diagnostics);
 
   const resourceProcessor = new Translator(
       [
@@ -107,7 +145,7 @@ export function translateFiles({sourceRootPath, sourceFilePaths, translationFile
       ],
       diagnostics);
 
-  const translations = translationLoader.loadBundles(translationFilePaths);
+  const translations = translationLoader.loadBundles(translationFilePaths, translationFileLocales);
   sourceRootPath = resolve(sourceRootPath);
   resourceProcessor.translateFiles(
       sourceFilePaths, sourceRootPath, outputPathFn, translations, sourceLocale);
diff --git a/packages/localize/src/tools/src/translate/source_files/source_file_translation_handler.ts b/packages/localize/src/tools/src/translate/source_files/source_file_translation_handler.ts
index 391f568eec7aa..0cf4906d41663 100644
--- a/packages/localize/src/tools/src/translate/source_files/source_file_translation_handler.ts
+++ b/packages/localize/src/tools/src/translate/source_files/source_file_translation_handler.ts
@@ -5,23 +5,18 @@
  * Use of this source code is governed by an MIT-style license that can be
  * found in the LICENSE file at https://angular.io/license
  */
-import {ɵMessageId, ɵParsedTranslation} from '@angular/localize/private';
 import {parseSync, transformFromAstSync} from '@babel/core';
 import {File, Program} from '@babel/types';
 import {extname, join} from 'path';
-
 import {Diagnostics} from '../../diagnostics';
 import {FileUtils} from '../../file_utils';
 import {OutputPathFn} from '../output_path';
 import {TranslationBundle, TranslationHandler} from '../translator';
-
 import {makeEs2015TranslatePlugin} from './es2015_translate_plugin';
 import {makeEs5TranslatePlugin} from './es5_translate_plugin';
 import {makeLocalePlugin} from './locale_plugin';
 import {TranslatePluginOptions} from './source_file_utils';
 
-
-
 /**
  * Translate a file by inlining all messages tagged by `$localize` with the appropriate translated
  * message.
diff --git a/packages/localize/src/tools/src/translate/translation_files/translation_file_loader.ts b/packages/localize/src/tools/src/translate/translation_files/translation_file_loader.ts
deleted file mode 100644
index 04cbc7bb3a51f..0000000000000
--- a/packages/localize/src/tools/src/translate/translation_files/translation_file_loader.ts
+++ /dev/null
@@ -1,34 +0,0 @@
-/**
- * @license
- * Copyright Google Inc. All Rights Reserved.
- *
- * Use of this source code is governed by an MIT-style license that can be
- * found in the LICENSE file at https://angular.io/license
- */
-import {FileUtils} from '../../file_utils';
-import {TranslationBundle} from '../translator';
-import {TranslationParser} from './translation_parsers/translation_parser';
-
-/**
- * Use this class to load a collection of translation files from disk.
- */
-export class TranslationLoader {
-  constructor(private translationParsers: TranslationParser[]) {}
-
-  /**
-   * Load and parse the translation files into a collection of `TranslationBundles`.
-   *
-   * @param translationFilePaths A collection of absolute paths to the translation files.
-   */
-  loadBundles(translationFilePaths: string[]): TranslationBundle[] {
-    return translationFilePaths.map(filePath => {
-      const fileContents = FileUtils.readFile(filePath);
-      for (const translationParser of this.translationParsers) {
-        if (translationParser.canParse(filePath, fileContents)) {
-          return translationParser.parse(filePath, fileContents);
-        }
-      }
-      throw new Error(`Unable to parse translation file: ${filePath}`);
-    });
-  }
-}
diff --git a/packages/localize/src/tools/src/translate/translation_files/translation_loader.ts b/packages/localize/src/tools/src/translate/translation_files/translation_loader.ts
new file mode 100644
index 0000000000000..33096987b111b
--- /dev/null
+++ b/packages/localize/src/tools/src/translate/translation_files/translation_loader.ts
@@ -0,0 +1,58 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+import {Diagnostics} from '../../diagnostics';
+import {FileUtils} from '../../file_utils';
+import {TranslationBundle} from '../translator';
+import {TranslationParser} from './translation_parsers/translation_parser';
+
+/**
+ * Use this class to load a collection of translation files from disk.
+ */
+export class TranslationLoader {
+  constructor(private translationParsers: TranslationParser[], private diagnostics: Diagnostics) {}
+
+  /**
+   * Load and parse the translation files into a collection of `TranslationBundles`.
+   *
+   * If there is a locale provided in `translationFileLocales` then this is used rather than the
+   * locale extracted from the file itself.
+   * If there is neither a provided locale nor a locale parsed from the file, then an error is
+   * thrown.
+   * If there are both a provided locale and a locale parsed from the file, and they are not the
+   * same, then a warning is reported .
+   *
+   * @param translationFilePaths An array of absolute paths to the translation files.
+   * @param translationFileLocales An array of locales for each of the translation files.
+   */
+  loadBundles(translationFilePaths: string[], translationFileLocales: (string|undefined)[]):
+      TranslationBundle[] {
+    return translationFilePaths.map((filePath, index) => {
+      const fileContents = FileUtils.readFile(filePath);
+      for (const translationParser of this.translationParsers) {
+        if (translationParser.canParse(filePath, fileContents)) {
+          const providedLocale = translationFileLocales[index];
+          const {locale: parsedLocale, translations} =
+              translationParser.parse(filePath, fileContents);
+          const locale = providedLocale || parsedLocale;
+          if (locale === undefined) {
+            throw new Error(
+                `The translation file "${filePath}" does not contain a target locale and no explicit locale was provided for this file.`);
+          }
+          if (parsedLocale !== undefined && providedLocale !== undefined &&
+              parsedLocale !== providedLocale) {
+            this.diagnostics.warn(
+                `The provided locale "${providedLocale}" does not match the target locale "${parsedLocale}" found in the translation file "${filePath}".`);
+          }
+          return {locale, translations};
+        }
+      }
+      throw new Error(
+          `There is no "TranslationParser" that can parse this translation file: ${filePath}.`);
+    });
+  }
+}
diff --git a/packages/localize/src/tools/src/translate/translation_files/translation_parsers/simple_json/simple_json_translation_parser.ts b/packages/localize/src/tools/src/translate/translation_files/translation_parsers/simple_json/simple_json_translation_parser.ts
index d5de42d1529c0..4e9f6d576e78b 100644
--- a/packages/localize/src/tools/src/translate/translation_files/translation_parsers/simple_json/simple_json_translation_parser.ts
+++ b/packages/localize/src/tools/src/translate/translation_files/translation_parsers/simple_json/simple_json_translation_parser.ts
@@ -7,8 +7,7 @@
  */
 import {ɵMessageId, ɵParsedTranslation, ɵparseTranslation} from '@angular/localize';
 import {extname} from 'path';
-import {TranslationBundle} from '../../../translator';
-import {TranslationParser} from '../translation_parser';
+import {ParsedTranslationBundle, TranslationParser} from '../translation_parser';
 
 /**
  * A translation parser that can parse JSON that has the form:
@@ -26,13 +25,13 @@ import {TranslationParser} from '../translation_parser';
 export class SimpleJsonTranslationParser implements TranslationParser {
   canParse(filePath: string, _contents: string): boolean { return (extname(filePath) === '.json'); }
 
-  parse(_filePath: string, contents: string): TranslationBundle {
-    const {locale, translations} = JSON.parse(contents);
+  parse(_filePath: string, contents: string): ParsedTranslationBundle {
+    const {locale: parsedLocale, translations} = JSON.parse(contents);
     const parsedTranslations: Record<ɵMessageId, ɵParsedTranslation> = {};
     for (const messageId in translations) {
       const targetMessage = translations[messageId];
       parsedTranslations[messageId] = ɵparseTranslation(targetMessage);
     }
-    return {locale, translations: parsedTranslations};
+    return {locale: parsedLocale, translations: parsedTranslations};
   }
 }
diff --git a/packages/localize/src/tools/src/translate/translation_files/translation_parsers/translation_parser.ts b/packages/localize/src/tools/src/translate/translation_files/translation_parsers/translation_parser.ts
index 144058d1b3595..802e6dfd7d377 100644
--- a/packages/localize/src/tools/src/translate/translation_files/translation_parsers/translation_parser.ts
+++ b/packages/localize/src/tools/src/translate/translation_files/translation_parsers/translation_parser.ts
@@ -5,7 +5,15 @@
  * Use of this source code is governed by an MIT-style license that can be
  * found in the LICENSE file at https://angular.io/license
  */
-import {TranslationBundle} from '../../translator';
+import {ɵMessageId, ɵParsedTranslation} from '@angular/localize/private';
+
+/**
+* An object that holds translations that have been parsed from a translation file.
+*/
+export interface ParsedTranslationBundle {
+  locale: string|undefined;
+  translations: Record<ɵMessageId, ɵParsedTranslation>;
+}
 
 /**
  * Implement this interface to provide a class that can parse the contents of a translation file.
@@ -25,5 +33,5 @@ export interface TranslationParser {
    * @param filePath The absolute path to the translation file.
    * @param contents The contents of the translation file.
    */
-  parse(filePath: string, contents: string): TranslationBundle;
+  parse(filePath: string, contents: string): ParsedTranslationBundle;
 }
diff --git a/packages/localize/src/tools/src/translate/translation_files/translation_parsers/xliff1/xliff1_translation_parser.ts b/packages/localize/src/tools/src/translate/translation_files/translation_parsers/xliff1/xliff1_translation_parser.ts
index 7679f618011b3..34e18da458bfb 100644
--- a/packages/localize/src/tools/src/translate/translation_files/translation_parsers/xliff1/xliff1_translation_parser.ts
+++ b/packages/localize/src/tools/src/translate/translation_files/translation_parsers/xliff1/xliff1_translation_parser.ts
@@ -9,11 +9,10 @@ import {Element, Node, XmlParser, visitAll} from '@angular/compiler';
 import {ɵMessageId, ɵParsedTranslation} from '@angular/localize';
 import {extname} from 'path';
 import {TargetMessageRenderer} from '../../../message_renderers/target_message_renderer';
-import {TranslationBundle} from '../../../translator';
 import {BaseVisitor} from '../base_visitor';
 import {TranslationParseError} from '../translation_parse_error';
-import {TranslationParser} from '../translation_parser';
-import {getAttrOrThrow, parseInnerRange} from '../translation_utils';
+import {ParsedTranslationBundle, TranslationParser} from '../translation_parser';
+import {getAttrOrThrow, getAttribute, parseInnerRange} from '../translation_utils';
 import {Xliff1MessageSerializer} from './xliff1_message_serializer';
 
 const XLIFF_1_2_NS_REGEX = /xmlns="urn:oasis:names:tc:xliff:document:1.2"/;
@@ -30,7 +29,7 @@ export class Xliff1TranslationParser implements TranslationParser {
     return (extname(filePath) === '.xlf') && XLIFF_1_2_NS_REGEX.test(contents);
   }
 
-  parse(filePath: string, contents: string): TranslationBundle {
+  parse(filePath: string, contents: string): ParsedTranslationBundle {
     const xmlParser = new XmlParser();
     const xml = xmlParser.parse(contents, filePath);
     const bundle = XliffFileElementVisitor.extractBundle(xml.rootNodes);
@@ -42,9 +41,9 @@ export class Xliff1TranslationParser implements TranslationParser {
 }
 
 class XliffFileElementVisitor extends BaseVisitor {
-  private bundle: TranslationBundle|undefined;
+  private bundle: ParsedTranslationBundle|undefined;
 
-  static extractBundle(xliff: Node[]): TranslationBundle|undefined {
+  static extractBundle(xliff: Node[]): ParsedTranslationBundle|undefined {
     const visitor = new this();
     visitAll(visitor, xliff);
     return visitor.bundle;
@@ -53,7 +52,7 @@ class XliffFileElementVisitor extends BaseVisitor {
   visitElement(element: Element): any {
     if (element.name === 'file') {
       this.bundle = {
-        locale: getAttrOrThrow(element, 'target-language'),
+        locale: getAttribute(element, 'target-language'),
         translations: XliffTranslationVisitor.extractTranslations(element)
       };
     } else {
diff --git a/packages/localize/src/tools/src/translate/translation_files/translation_parsers/xliff2/xliff2_translation_parser.ts b/packages/localize/src/tools/src/translate/translation_files/translation_parsers/xliff2/xliff2_translation_parser.ts
index 6167c9fcacfd6..57d9c402ec325 100644
--- a/packages/localize/src/tools/src/translate/translation_files/translation_parsers/xliff2/xliff2_translation_parser.ts
+++ b/packages/localize/src/tools/src/translate/translation_files/translation_parsers/xliff2/xliff2_translation_parser.ts
@@ -9,11 +9,10 @@ import {Element, Node, XmlParser, visitAll} from '@angular/compiler';
 import {ɵMessageId, ɵParsedTranslation} from '@angular/localize';
 import {extname} from 'path';
 import {TargetMessageRenderer} from '../../../message_renderers/target_message_renderer';
-import {TranslationBundle} from '../../../translator';
 import {BaseVisitor} from '../base_visitor';
 import {TranslationParseError} from '../translation_parse_error';
-import {TranslationParser} from '../translation_parser';
-import {getAttrOrThrow, parseInnerRange} from '../translation_utils';
+import {ParsedTranslationBundle, TranslationParser} from '../translation_parser';
+import {getAttrOrThrow, getAttribute, parseInnerRange} from '../translation_utils';
 import {Xliff2MessageSerializer} from './xliff2_message_serializer';
 
 const XLIFF_2_0_NS_REGEX = /xmlns="urn:oasis:names:tc:xliff:document:2.0"/;
@@ -29,7 +28,7 @@ export class Xliff2TranslationParser implements TranslationParser {
     return (extname(filePath) === '.xlf') && XLIFF_2_0_NS_REGEX.test(contents);
   }
 
-  parse(filePath: string, contents: string): TranslationBundle {
+  parse(filePath: string, contents: string): ParsedTranslationBundle {
     const xmlParser = new XmlParser();
     const xml = xmlParser.parse(contents, filePath);
     const bundle = Xliff2TranslationBundleVisitor.extractBundle(xml.rootNodes);
@@ -40,27 +39,30 @@ export class Xliff2TranslationParser implements TranslationParser {
   }
 }
 
+interface BundleVisitorContext {
+  parsedLocale?: string;
+}
+
 class Xliff2TranslationBundleVisitor extends BaseVisitor {
-  private locale: string|undefined;
-  private bundle: TranslationBundle|undefined;
+  private bundle: ParsedTranslationBundle|undefined;
 
-  static extractBundle(xliff: Node[]): TranslationBundle|undefined {
+  static extractBundle(xliff: Node[]): ParsedTranslationBundle|undefined {
     const visitor = new this();
-    visitAll(visitor, xliff);
+    visitAll(visitor, xliff, {});
     return visitor.bundle;
   }
 
-  visitElement(element: Element): any {
+  visitElement(element: Element, {parsedLocale}: BundleVisitorContext): any {
     if (element.name === 'xliff') {
-      this.locale = getAttrOrThrow(element, 'trgLang');
-      return visitAll(this, element.children);
+      parsedLocale = getAttribute(element, 'trgLang');
+      return visitAll(this, element.children, {parsedLocale});
     } else if (element.name === 'file') {
       this.bundle = {
-        locale: this.locale !,
+        locale: parsedLocale,
         translations: Xliff2TranslationVisitor.extractTranslations(element)
       };
     } else {
-      return visitAll(this, element.children);
+      return visitAll(this, element.children, {parsedLocale});
     }
   }
 }
diff --git a/packages/localize/src/tools/src/translate/translator.ts b/packages/localize/src/tools/src/translate/translator.ts
index a99f1fdc138bd..1cda8b75d01f1 100644
--- a/packages/localize/src/tools/src/translate/translator.ts
+++ b/packages/localize/src/tools/src/translate/translator.ts
@@ -13,11 +13,8 @@ import {FileUtils} from '../file_utils';
 
 import {OutputPathFn} from './output_path';
 
-
-
 /**
- * An object that holds translations that have been loaded
- * from a translation file.
+ * An object that holds information to be used to translate files.
  */
 export interface TranslationBundle {
   locale: string;
diff --git a/packages/localize/src/tools/test/translate/integration/main_spec.ts b/packages/localize/src/tools/test/translate/integration/main_spec.ts
index bfaecaacf2fb9..8fdb9bdbc2bff 100644
--- a/packages/localize/src/tools/test/translate/integration/main_spec.ts
+++ b/packages/localize/src/tools/test/translate/integration/main_spec.ts
@@ -30,7 +30,7 @@ describe('translateFiles()', () => {
       outputPathFn,
       translationFilePaths: resolveAll(
           __dirname + '/locales', ['messages.de.json', 'messages.es.xlf', 'messages.fr.xlf']),
-      diagnostics,
+      translationFileLocales: [], diagnostics,
       missingTranslation: 'error'
     });
 
@@ -58,7 +58,7 @@ describe('translateFiles()', () => {
       sourceFilePaths: resolveAll(__dirname + '/test_files', ['test.js']), outputPathFn,
       translationFilePaths: resolveAll(
           __dirname + '/locales', ['messages.de.json', 'messages.es.xlf', 'messages.fr.xlf']),
-      diagnostics,
+      translationFileLocales: [], diagnostics,
       missingTranslation: 'error',
     });
 
@@ -72,6 +72,33 @@ describe('translateFiles()', () => {
         .toEqual(`var name="World";var message="Hola, "+name+"!";`);
   });
 
+  it('should translate and copy source-code files overriding the locales', () => {
+    const diagnostics = new Diagnostics();
+    const outputPathFn = getOutputPathFn(resolve(testDir, '{{LOCALE}}'));
+    translateFiles({
+      sourceRootPath: resolve(__dirname, 'test_files'),
+      sourceFilePaths: resolveAll(__dirname + '/test_files', ['test.js']), outputPathFn,
+      translationFilePaths: resolveAll(
+          __dirname + '/locales', ['messages.de.json', 'messages.es.xlf', 'messages.fr.xlf']),
+      translationFileLocales: ['xde', undefined, 'fr'], diagnostics,
+      missingTranslation: 'error',
+    });
+
+    expect(diagnostics.messages.length).toEqual(1);
+    expect(diagnostics.messages).toContain({
+      type: 'warning',
+      message:
+          `The provided locale "xde" does not match the target locale "de" found in the translation file "${resolve(__dirname, 'locales', 'messages.de.json')}".`
+    });
+
+    expect(FileUtils.readFile(resolve(testDir, 'xde', 'test.js')))
+        .toEqual(`var name="World";var message="Guten Tag, "+name+"!";`);
+    expect(FileUtils.readFile(resolve(testDir, 'es', 'test.js')))
+        .toEqual(`var name="World";var message="Hola, "+name+"!";`);
+    expect(FileUtils.readFile(resolve(testDir, 'fr', 'test.js')))
+        .toEqual(`var name="World";var message="Bonjour, "+name+"!";`);
+  });
+
   it('should transform and/or copy files to the destination folders', () => {
     const diagnostics = new Diagnostics();
     const outputPathFn = getOutputPathFn(resolve(testDir, '{{LOCALE}}'));
@@ -82,7 +109,7 @@ describe('translateFiles()', () => {
       outputPathFn,
       translationFilePaths: resolveAll(
           __dirname + '/locales', ['messages.de.json', 'messages.es.xlf', 'messages.fr.xlf']),
-      diagnostics,
+      translationFileLocales: [], diagnostics,
       missingTranslation: 'error',
     });
 
diff --git a/packages/localize/src/tools/test/translate/translation_files/translation_loader_spec.ts b/packages/localize/src/tools/test/translate/translation_files/translation_loader_spec.ts
index 9f7497c152e06..0fd0a5c29983c 100644
--- a/packages/localize/src/tools/test/translate/translation_files/translation_loader_spec.ts
+++ b/packages/localize/src/tools/test/translate/translation_files/translation_loader_spec.ts
@@ -7,8 +7,9 @@
  */
 import {ɵParsedTranslation} from '@angular/localize';
 
+import {Diagnostics} from '../../../src/diagnostics';
 import {FileUtils} from '../../../src/file_utils';
-import {TranslationLoader} from '../../../src/translate/translation_files/translation_file_loader';
+import {TranslationLoader} from '../../../src/translate/translation_files/translation_loader';
 import {TranslationParser} from '../../../src/translate/translation_files/translation_parsers/translation_parser';
 
 describe('TranslationLoader', () => {
@@ -18,9 +19,10 @@ describe('TranslationLoader', () => {
     });
 
     it('should `canParse()` and `parse()` for each file', () => {
-      const parser = new MockTranslationParser(true);
-      const loader = new TranslationLoader([parser]);
-      loader.loadBundles(['/src/locale/messages.en.xlf', '/src/locale/messages.fr.xlf']);
+      const diagnostics = new Diagnostics();
+      const parser = new MockTranslationParser(true, 'fr');
+      const loader = new TranslationLoader([parser], diagnostics);
+      loader.loadBundles(['/src/locale/messages.en.xlf', '/src/locale/messages.fr.xlf'], []);
       expect(parser.log).toEqual([
         'canParse(/src/locale/messages.en.xlf, english messages)',
         'parse(/src/locale/messages.en.xlf, english messages)',
@@ -30,11 +32,12 @@ describe('TranslationLoader', () => {
     });
 
     it('should stop at the first parser that can parse each file', () => {
+      const diagnostics = new Diagnostics();
       const parser1 = new MockTranslationParser(false);
-      const parser2 = new MockTranslationParser(true);
-      const parser3 = new MockTranslationParser(true);
-      const loader = new TranslationLoader([parser1, parser2, parser3]);
-      loader.loadBundles(['/src/locale/messages.en.xlf', '/src/locale/messages.fr.xlf']);
+      const parser2 = new MockTranslationParser(true, 'fr');
+      const parser3 = new MockTranslationParser(true, 'en');
+      const loader = new TranslationLoader([parser1, parser2, parser3], diagnostics);
+      loader.loadBundles(['/src/locale/messages.en.xlf', '/src/locale/messages.fr.xlf'], []);
       expect(parser1.log).toEqual([
         'canParse(/src/locale/messages.en.xlf, english messages)',
         'canParse(/src/locale/messages.fr.xlf, french messages)',
@@ -49,22 +52,64 @@ describe('TranslationLoader', () => {
 
     it('should return locale and translations parsed from each file', () => {
       const translations = {};
+      const diagnostics = new Diagnostics();
       const parser = new MockTranslationParser(true, 'pl', translations);
-      const loader = new TranslationLoader([parser]);
+      const loader = new TranslationLoader([parser], diagnostics);
       const result =
-          loader.loadBundles(['/src/locale/messages.en.xlf', '/src/locale/messages.fr.xlf']);
+          loader.loadBundles(['/src/locale/messages.en.xlf', '/src/locale/messages.fr.xlf'], []);
       expect(result).toEqual([
         {locale: 'pl', translations},
         {locale: 'pl', translations},
       ]);
     });
 
+    it('should return the provided locale if there is no parsed locale', () => {
+      const translations = {};
+      const diagnostics = new Diagnostics();
+      const parser = new MockTranslationParser(true, undefined, translations);
+      const loader = new TranslationLoader([parser], diagnostics);
+      const result = loader.loadBundles(
+          ['/src/locale/messages.en.xlf', '/src/locale/messages.fr.xlf'], ['en', 'fr']);
+      expect(result).toEqual([
+        {locale: 'en', translations},
+        {locale: 'fr', translations},
+      ]);
+    });
+
+    it('should warn if the provided locales do not match the parsed locales', () => {
+      const translations = {};
+      const diagnostics = new Diagnostics();
+      const parser = new MockTranslationParser(true, 'pl', translations);
+      const loader = new TranslationLoader([parser], diagnostics);
+      loader.loadBundles(
+          ['/src/locale/messages.en.xlf', '/src/locale/messages.fr.xlf'], [undefined, 'FR']);
+      expect(diagnostics.messages.length).toEqual(1);
+      expect(diagnostics.messages).toContain({
+        type: 'warning',
+        message:
+            `The provided locale "FR" does not match the target locale "pl" found in the translation file "/src/locale/messages.fr.xlf".`,
+      }, );
+    });
+
+    it('should throw an error if there is no provided nor parsed target locale', () => {
+      const translations = {};
+      const diagnostics = new Diagnostics();
+      const parser = new MockTranslationParser(true, undefined, translations);
+      const loader = new TranslationLoader([parser], diagnostics);
+      expect(() => loader.loadBundles(['/src/locale/messages.en.xlf'], []))
+          .toThrowError(
+              'The translation file "/src/locale/messages.en.xlf" does not contain a target locale and no explicit locale was provided for this file.');
+    });
+
     it('should error if none of the parsers can parse the file', () => {
+      const diagnostics = new Diagnostics();
       const parser = new MockTranslationParser(false);
-      const loader = new TranslationLoader([parser]);
-      expect(() => loader.loadBundles([
-        '/src/locale/messages.en.xlf', '/src/locale/messages.fr.xlf'
-      ])).toThrowError('Unable to parse translation file: /src/locale/messages.en.xlf');
+      const loader = new TranslationLoader([parser], diagnostics);
+      expect(
+          () => loader.loadBundles(
+              ['/src/locale/messages.en.xlf', '/src/locale/messages.fr.xlf'], []))
+          .toThrowError(
+              'There is no "TranslationParser" that can parse this translation file: /src/locale/messages.en.xlf.');
     });
   });
 });
@@ -72,7 +117,7 @@ describe('TranslationLoader', () => {
 class MockTranslationParser implements TranslationParser {
   log: string[] = [];
   constructor(
-      private _canParse: boolean = true, private _locale: string = 'fr',
+      private _canParse: boolean = true, private _locale?: string,
       private _translations: Record<string, ɵParsedTranslation> = {}) {}
 
   canParse(filePath: string, fileContents: string) {
diff --git a/packages/localize/src/tools/test/translate/translation_files/translation_parsers/xliff1/xliff1_translation_parser_spec.ts b/packages/localize/src/tools/test/translate/translation_files/translation_parsers/xliff1/xliff1_translation_parser_spec.ts
index 972f33dbae81e..f8a25dc3fdc8c 100644
--- a/packages/localize/src/tools/test/translate/translation_files/translation_parsers/xliff1/xliff1_translation_parser_spec.ts
+++ b/packages/localize/src/tools/test/translate/translation_files/translation_parsers/xliff1/xliff1_translation_parser_spec.ts
@@ -40,6 +40,19 @@ describe('Xliff1TranslationParser', () => {
       expect(result.locale).toEqual('fr');
     });
 
+    it('should return an undefined locale if there is no locale in the file', () => {
+      const XLIFF = `
+      <xliff version="1.2" xmlns="urn:oasis:names:tc:xliff:document:1.2">
+        <file source-language="en" datatype="plaintext" original="ng2.template">
+          <body>
+          </body>
+        </file>
+      </xliff>`;
+      const parser = new Xliff1TranslationParser();
+      const result = parser.parse('/some/file.xlf', XLIFF);
+      expect(result.locale).toBeUndefined();
+    });
+
     it('should extract basic messages', () => {
       /**
        * Source HTML:
diff --git a/packages/localize/src/tools/test/translate/translation_files/translation_parsers/xliff2/xliff2_translation_parser_spec.ts b/packages/localize/src/tools/test/translate/translation_files/translation_parsers/xliff2/xliff2_translation_parser_spec.ts
index d31f56c6d4af2..94bb19e45b8a0 100644
--- a/packages/localize/src/tools/test/translate/translation_files/translation_parsers/xliff2/xliff2_translation_parser_spec.ts
+++ b/packages/localize/src/tools/test/translate/translation_files/translation_parsers/xliff2/xliff2_translation_parser_spec.ts
@@ -39,6 +39,17 @@ describe('Xliff2TranslationParser', () => {
       expect(result.locale).toEqual('fr');
     });
 
+    it('should return undefined locale if there is no locale in the file', () => {
+      const XLIFF = `
+      <xliff version="2.0" xmlns="urn:oasis:names:tc:xliff:document:2.0" srcLang="en">
+        <file original="ng.template" id="ngi18n">
+        </file>
+      </xliff>`;
+      const parser = new Xliff2TranslationParser();
+      const result = parser.parse('/some/file.xlf', XLIFF);
+      expect(result.locale).toBeUndefined();
+    });
+
     it('should extract basic messages', () => {
       /**
        * Source HTML: