[HttpKernel] Accept-Language and defaultLocale

[karimmorel]

Q	A
Branch	5.4
Bug fix	yes
New feature	no
Deprecations	no
License	MIT

When the Accept-Language header is used to set the locale, if it's value is not within the list of enabled_locales, the value for default_locale is overwritten by the first value of the list of enabled_locales.

[carsonbot]

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[rosier]

This looks more like a configuration issue to me. For this feature the order of locales is important.

https://symfony.com/doc/current/translation.html#selecting-the-language-preferred-by-the-user

[Seb33300]

Indeed, just found this in the documentation.

If it can't find a perfect match between them, this method returns the first locale passed as argument (that's why the order of the passed locales is important).

However, this behaviour looks wrong to me.
IMO, if it can't find a perfect match, I think it should return the default locale, not the first of the list.

And this PR fixes the issue by setting the default locale first in the list.

[rosier]

I may be missing something, but can't you put in your config the default as the first value of the list of enabled_locales

[karimmorel]

I was not aware of that part of the documentation, but when I noticed that behaviour, I thought it was weirdly designed.

default_locale is used to set the locale, while enabled_locales is used to limit it. So to me, it is weird to use enabled_locales to set the locale.

[Seb33300]

@karimmorel you should also open a PR to update the documentation in case this PR is merged:
https://github.com/symfony/symfony-docs/edit/6.4/translation.rst

[Seb33300]

Just realized that the documentation concerns the method getPreferredLanguage() and you did not change that method.
So you dont need to update the doc.