Add language name translated into active language to LANG_INFO dictionary

[Tomáš Ehrlich]

get_language_info tag returns english name and local name of language:

language.local_name == česky
language.name == Czech

Neither depends on active language, but sometimes there's need for translated language name, ex. tchèque (in French). The only way how to do it right now is to take the english name and run it through gettext since Django already has all languages translated.

This would be very handy filter tag:

@register.filter
def language_translated(code):
    """
    Return language name translated into active language
    """

    name = translation.get_language_info(code)['name'].capitalize()
    return translation.gettext(name)

---

Maybe we could also extend dictionary returned by the get_language_info tag with name_translated to keep API consistent. All keys from get_language_info have matching filter variants (language_name, language_name_local and language_bidi).

[Wim Feijen]

Accepted because not all people are English.

[Tomáš Ehrlich]

Added PR ​https://github.com/django/django/pull/3997 with proposal.

I'm not sure if we should name it name_translated. It's a bit log and it would make sense to simply translate name directly. However, that would be backward incompatible. Add new item to LANG_INFO dictionary is less invasive.

Missing documentation update and tests for filter.

[Tomáš Ehrlich]

Documentation updated, but there's some build error. I can't see it now, the page is blocked at Cardiff University

[Tim Graham <timograham@…>]

In 002b3d8:

Fixed #24230 -- Added translated language name for i18n template tag/filter.