Why is accept-languages not evaluated?

[LostKobrakai]

Your expectation is not correct. There are no attempts made by phoenix nor gettext to deal with accept language headers.

For an implementation of such you can look at:

https://hexdocs.pm/ex_cldr/Cldr.Plug.AcceptLanguage.html#content

Edit:
Seems like cowlib can also parse the header:

Is there an Hex package to parse "Accept-Language" header?

As @g-andrade said, we can use cowlib. accept_language = "ja,en-US;q=0.9,en;q=0.8,zh-CN;q=0.7,zh;q=0.6" :cow_http_hd.parse_accept_language(accept_language) This code returns [{"ja", 1000}, {"en-us", 900}, {"en", 800}, {"zh-cn", 700}, {"zh", 600}]. Note that the cowlib converts all letters in the country code to lowercase.