Documentation for 'language' form type misleading

[cblegare]

As stated in this documentation page

The "value" for each language is the Unicode language identifier (e.g. fr or zh-Hant).

which is wrong. Symfony uses some custom standard using underscores, not dashes, for languages.

[cblegare]

IMO, this is not a documentation issue. This is only my opinion ;)

[stof]

Well, the issue is that the documentation is wrong currently. It does not document the actual behavior of the code, while it should