Transifex is an online website aimed at offering easy translation for various contents. Transifex service is free for OpenSource project.
J!TrackGallery is registered on Transifex.com. In order to translate J!TrackGallery in any language you should:
Any Translation made on Transifex will be included in the next published version of J!TrackGallery. You can also, download recently modified language files and add them to your Joomla installation in order.
When using file downloaded from Transifex, under Joomla 2.x, some untranslated key will appear like COM_JTG_BICYCLE because J!2.X do not systematically load default english language before your selected language.