Add a way to assign tags to languages

[Jerska]

Zendesk doesn't provide a way to have tags per language. Since we're displaying them publicly, we should provide a way for our users to have tags per language.

A syntax like locale:tag would probably do the trick. We would still index tags without the delimiter for all translations.

[redox]

Looks good 👍

I'm sure there is no way someone has a regular tag starting by a locale + : so we can even deploy it in a minor release 👍

[Jerska]

Done with 2.8.0 .