Allow localization of language names in multisite

[pavelevap]

There is Site Language settings in multisite (General Options). But all available languages are in English, so there is English, Czech, etc. But when I switch to Czech language, there is still only Czech and not "Čeština". I am not sure if there is need to translate all languages, but there should be localized at least selected language (or all available languages).

It is caused by function format_code_lang() in ms.php (line 463) where are all language names hardcoded in English.

[vanillalounge]

This may warrant a separate ticket, but it seems that the list is hardcoded, with a set of locales which is partly out of date (example: no value for Brazilian Portuguese, pt_BR)

[ramiy]

more info:
​http://wppolyglots.wordpress.com/2012/06/06/is-it-possible-to-translate-the-word/

and:
​http://core.trac.wordpress.org/browser/trunk/wp-admin/includes/ms.php#L423

[pavelevap]

Related: #13069

[ocean90]

In 29630:

Language packs: No WPLANG anymore.

• The WPLANG constant is no longer needed. Remove define('WPLANG', ); from wp-config-sample.php. Populate WPLANG option based on the WPLANG constant. When get_option('WPLANG') is an empty string it will override WPLANG.
• Introduce translations_api() which is available to communicate with the translation API. Move translation install related functions to a new file.
• Replace mu_dropdown_languages() with wp_dropdown_languages(). wp_dropdown_languages() is now populated by the translation API.
• Remove wp_install_load_language() and allow load_default_textdomain() to switch a core translation.

fixes #13069, #15677, #19760, #28730, #29281.