SInce this topic has been somewhat inconclusive I’d like to return to what I think was an excellent suggestion:
This would be immensely helpful and as far as I can tell (which is not very far) it’s probably a rather easy thing to accomplish. Any chance that this could get implemented?
Just to reiterate why this is useful, since the discussion above is somewhat complex: basically, it solves the problem that once you customize any text element in your site’s default language, you can no longer allow users to choose their own locale (let alone enable set locale from accept language header) because they will be seeing the default texts in their respective language and those will no longer correspond to the texts in the site’s main language.
I should add one important detail to the proposed solution:
if you customize a translation of the default site locale, all the other locales should treat its corresponding translation text as missing unless the translation text has also been customized
In other words: if my site is in English and I customized a specific text in English but also in French, all locales will fall back to the default locale for that specific text except for the French locale, (because it has also been customized so that a correspondence between the translations can be assumed).