Hi envisionmedia ,
We do have this feature request high on the wish list and will probably be implement after the big 2.1 update which will become available within a few months.
There is a solution for this now if you have the premium version of Buttonizer. Then you're able to archive something similar using page rules. You only show a specific button group for a specific language URL, using the 'url starts with'.
Then you can create two page rules. One which will be triggered when the URL starts with '/en', and the other one triggers on '/fr' for example. This solution is depending on how the URL looks.
Does this help?