J!TrackGallery fully supports multiple language as long as translation files are provided and you use a language switcher plugin.
Since J!TrackGallery 0.9.22, we use Transifex for J!TrackGallery project translation
Full up to date available languages list is avalable at Transifex.
By default, J!TrackGallery use english language for each key which is not translated in your language. In any case knowing a little of english you will be able to start using J!TrackGallery without a complete translation set.
J!TrackGallery code do not account for RTL language. At present the developper team has no experience in this field, however anyone interested is encouraged to join us.