Add list of Tor Browser's supported locales to support portal

The support article for "I need Tor Browser in a language that's not English" currently points readers towards /download/languages/ to find out what languages Tor Browser supports. However these builds will cease to exist when multi-locale bundles hit stable in Tor Browser 12.0, and it's possible we'll replace that page entirely with a redirect.

Could we maintain a list of locales in a user-friendly manner here instead please? This would also come in useful on the download pages too, so that we have a reference point we can link users to after the full list of localized bundles have been removed.

For example, see the (temporary) changes proposed for Alpha here: tpo#330 (comment 2848986)