There already is the same thing for Wiktionary. See "More extensions by..." Since a few days ago, it is not showing the language buttons. I guess this is because they changed HTML. I will fix that in a few days.
The problem is that French Wikipedia/Wiktionary started using weird HTML that are different from other languages like English or Japanese. Making my extensions work with French was complicated than I thought, so I had been working on that (but stopped to do other things).