Multisite: Add missing options to the list of languages

[henry.wright]

In a network install go to Settings > Network Settings and then scroll down to the "Language Settings" section. The option list of languages doesn't include all languages available at ​https://translate.wordpress.org/

For example, Oriya (Odia) and Malagasy can't be selected as the default language because they aren't in the list. These are the 2 languages I noticed but there may be more languages missing

I am reporting this here based on a comment by @johnbillion in ​https://core.trac.wordpress.org/ticket/51382

[ocean90]

See my comment on the core ticket, locales need to have the translation completed at least once for the current or a previous version of WordPress.