Upto now Gmail Labs has been, well, a lab, an experiment and was available only in English. However, with the increased popularity of Gmail Labs products like Offline Access, Undo Sent, Multiple Inbox etc., it has now been made global just like any other google products.
Gmail Labs now supports all the languages supported by Google with the exception of three - Hebrew, Arabic, and Urdu. That is a total of 49 languages. Now, you will get all the Lab products in the language you choosed.
However, Gmail Labs is still an experiment and Google concede that they may break and should not be treated like the other products.
You can read the original post in the Gmail blog here.