Twitter is continuing to add even more translations. The site really is on its way of becoming truly global but localized. It is adding these translations in batches, several languages at a time, as soon as they become available. The site relies on volunteer translators for all of the languages.
The latest addition is support for Basque, Czech and Greek. Users who want these languages can now go to the Twitter settings and pick any of them. The languages are still labeled as "beta" but support should be pretty solid at this point.
Twitter added five languages to its Translation Center in May. The first two were completed in July
, these last three are now available meaning that a new a whole new batch is on its way. The languages that Twitter would want translated next should be announced soon and you'll be able to get involved if you want to help.