Add locale-filter to Search Interface

[rmzelle]

It would be nice if users could filter styles on the language specified in default-locale. I think a dropdown-menu would suffice.

If limited to the first two characters of the locale code (e.g. "en" for "en-US", "en-GB" and "en"), the number of different languages isn't that big. https://github.com/citation-style-language/locales/blob/master/locales.json provides a conversion table between locale codes and English language names.

See also http://xbiblio-devel.2463403.n2.nabble.com/Filter-by-locale-in-Zotero-Style-Repository-td7578322.html

[rmzelle]

I still think this is valuable since it's not immediately obvious to users that they have to type in English language names ("German" instead of "Deutsch"). We also currently don't automatically check whether all styles with a default-locale attribute mention the locale name in the title, so relying on default-locale would be more reliable.

We would just have to make it clear somehow that language-agnostic styles (without a default-locale) can also be used for the locale of interest.

[zuphilip]

I agree that language would be a useful filter. However, I think that a clear handling of the language-agnostic (or call them language-independent?) styles is important. Maybe, we could have a list of all different languages AND an option to include/exclude language-agnostic styles.