feat: respect language preferences on Win/macOS

This commit partially fixes electron#18829

Chromium uses navigator.languages (Accept-Language) to determine
fallback fonts on Windows, especially kanji/han characters in CJK.

Previously the full preferences set to OS was not given to Chromium.
For instance, when user sets 'en-US, ja-JP' to Accept-Language,
while Chromium chooses Japanese font for kanji text, but Electron
chooses Chinese font.  This is because only the first language is given
to Accept-Language on Electron.

This patch is based on electron#15532

Co-authored-by: Nitish Sakhawalkar <nitsakh@icloud.com>
Co-authored-by: Kasumi Hanazuki <kasumi@rollingapple.net>

filenames.gni

@@ -109,9 +109,11 @@ filenames = {
     "shell/browser/api/electron_api_web_contents.cc",
     "shell/browser/api/electron_api_web_contents.h",
     "shell/browser/api/electron_api_web_contents_impl.cc",
+    "shell/browser/api/electron_api_web_contents_linux.cc",
     "shell/browser/api/electron_api_web_contents_mac.mm",
     "shell/browser/api/electron_api_web_contents_view.cc",
     "shell/browser/api/electron_api_web_contents_view.h",
+    "shell/browser/api/electron_api_web_contents_win.cc",
     "shell/browser/api/electron_api_web_request.cc",
     "shell/browser/api/electron_api_web_request.h",
     "shell/browser/api/electron_api_web_view_manager.cc",

shell/browser/api/electron_api_web_contents.cc

@@ -100,6 +100,7 @@
 #include "third_party/blink/public/mojom/frame/find_in_page.mojom.h"
 #include "third_party/blink/public/mojom/frame/fullscreen.mojom.h"
 #include "third_party/blink/public/mojom/messaging/transferable_message.mojom.h"
+#include "third_party/blink/public/mojom/renderer_preferences.mojom.h"
 #include "ui/base/cursor/cursor.h"
 #include "ui/base/mojom/cursor_type.mojom-shared.h"
 #include "ui/display/screen.h"
@@ -121,7 +122,6 @@
 #endif
 
 #if defined(OS_LINUX) || defined(OS_WIN)
-#include "third_party/blink/public/mojom/renderer_preferences.mojom.h"
 #include "ui/gfx/font_render_params.h"
 #endif
 
@@ -535,7 +535,7 @@ void WebContents::InitWithSessionAndOptions(
   managed_web_contents()->GetView()->SetDelegate(this);
 
   auto* prefs = web_contents()->GetMutableRendererPrefs();
-  prefs->accept_languages = g_browser_process->GetApplicationLocale();
+  SetAcceptLanguages(prefs);
 
 #if defined(OS_LINUX) || defined(OS_WIN)
   // Update font settings.

shell/browser/api/electron_api_web_contents.h

@@ -579,6 +579,12 @@ class WebContents : public gin_helper::TrackableObject<WebContents>,
   void InitZoomController(content::WebContents* web_contents,
                           const gin_helper::Dictionary& options);
 
+  void SetAcceptLanguages(blink::mojom::RendererPreferences* prefs);
+#if defined(OS_WIN)
+  // Get OS preferred languages in Windows 10 or later
+  bool GetLanguagesUsingGlobalization(std::vector<base::string16>* languages);
+#endif
+
   v8::Global<v8::Value> session_;
   v8::Global<v8::Value> devtools_web_contents_;
   v8::Global<v8::Value> debugger_;

shell/browser/api/electron_api_web_contents_linux.cc

@@ -0,0 +1,20 @@
+// Copyright (c) 2020 GitHub, Inc.
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+#include "shell/browser/api/electron_api_web_contents.h"
+
+#include "chrome/browser/browser_process.h"
+#include "third_party/blink/public/mojom/renderer_preferences.mojom.h"
+
+namespace electron {
+
+namespace api {
+
+void WebContents::SetAcceptLanguages(blink::mojom::RendererPreferences* prefs) {
+  prefs->accept_languages = g_browser_process->GetApplicationLocale();
+}
+
+}  // namespace api
+
+}  // namespace electron

shell/browser/api/electron_api_web_contents_mac.mm

@@ -2,8 +2,10 @@
 // Use of this source code is governed by the MIT license that can be
 // found in the LICENSE file.
 
+#include "base/strings/sys_string_conversions.h"
 #include "content/public/browser/render_widget_host_view.h"
 #include "shell/browser/api/electron_api_web_contents.h"
+#include "third_party/blink/public/mojom/renderer_preferences.mojom.h"
 
 #import <Cocoa/Cocoa.h>
 
@@ -27,6 +29,11 @@
   return view->HasFocus();
 }
 
+void WebContents::SetAcceptLanguages(blink::mojom::RendererPreferences* prefs) {
+  prefs->accept_languages = base::SysNSStringToUTF8(
+      [[NSLocale preferredLanguages] componentsJoinedByString:@","]);
+}
+
 }  // namespace api
 
 }  // namespace electron

shell/browser/api/electron_api_web_contents_win.cc

@@ -0,0 +1,82 @@
+// Copyright (c) 2020 GitHub, Inc.
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+#include "shell/browser/api/electron_api_web_contents.h"
+
+#include <roapi.h>
+#include <windows.system.userprofile.h>
+#include <wrl.h>
+
+#include "base/strings/sys_string_conversions.h"
+#include "base/win/core_winrt_util.h"
+#include "base/win/i18n.h"
+#include "base/win/win_util.h"
+#include "base/win/windows_version.h"
+#include "third_party/blink/public/mojom/renderer_preferences.mojom.h"
+
+namespace electron {
+
+namespace api {
+
+void WebContents::SetAcceptLanguages(blink::mojom::RendererPreferences* prefs) {
+  std::vector<base::string16> languages;
+
+  // Attempt to use API available on Windows 10 or later, which
+  // returns the full list of language preferences.
+  if (!GetLanguagesUsingGlobalization(&languages)) {
+    base::win::i18n::GetThreadPreferredUILanguageList(&languages);
+  }
+
+  std::string accept_langs;
+  for (const auto& language : languages) {
+    accept_langs += base::SysWideToUTF8(language) + ',';
+  }
+  accept_langs.pop_back();
+  prefs->accept_languages = accept_langs;
+}
+
+bool WebContents::GetLanguagesUsingGlobalization(
+    std::vector<base::string16>* languages) {
+  if (base::win::GetVersion() < base::win::Version::WIN10)
+    return false;
+  if (!base::win::ResolveCoreWinRTDelayload() ||
+      !base::win::ScopedHString::ResolveCoreWinRTStringDelayload())
+    return false;
+
+  base::win::ScopedHString guid = base::win::ScopedHString::Create(
+      RuntimeClass_Windows_System_UserProfile_GlobalizationPreferences);
+  Microsoft::WRL::ComPtr<
+      ABI::Windows::System::UserProfile::IGlobalizationPreferencesStatics>
+      prefs;
+
+  HRESULT hr =
+      base::win::RoGetActivationFactory(guid.get(), IID_PPV_ARGS(&prefs));
+  if (FAILED(hr))
+    return false;
+
+  ABI::Windows::Foundation::Collections::IVectorView<HSTRING>* langs;
+  hr = prefs->get_Languages(&langs);
+  if (FAILED(hr))
+    return false;
+
+  unsigned size;
+  hr = langs->get_Size(&size);
+  if (FAILED(hr))
+    return false;
+
+  for (unsigned i = 0; i < size; ++i) {
+    HSTRING hstr;
+    hr = langs->GetAt(i, &hstr);
+    if (SUCCEEDED(hr)) {
+      base::WStringPiece str = base::win::ScopedHString(hstr).Get();
+      languages->emplace_back(str.data(), str.size());
+    }
+  }
+
+  return true;
+}
+
+}  // namespace api
+
+}  // namespace electron

spec-main/chromium-spec.ts

@@ -319,7 +319,8 @@ describe('chromium features', () => {
       const w = new BrowserWindow({ show: false });
       await w.loadURL('about:blank');
       const languages = await w.webContents.executeJavaScript('navigator.languages');
-      expect(languages).to.deep.equal([appLocale]);
+      expect(languages.length).to.be.greaterThan(0);
+      expect(languages).to.contain(appLocale);
     });
   });