Вот такой вопрос возник.
Если в заголовках, Accept-Language: fr,ru;q=0.5,en;q=0.6, то в какой локали отдавать контент?
Нашёл пока мутный ответ, https://stackoverflow.com/questions/6548214/why-use-quality-values-in-the-htt...
«Interesting question. The discussion of how this feature came to be is probably buried somewhere in the mailing list archives, for which I could not find a valid link. Your example is not the only problematic one.»
