One closed comment, i found out now why it not works (in some module). They use content modules (content and dh-info from alfred] and they use the seo wrapper mode (site ends with .html).
At the moment you switch the mode to seo, the lang tags in the brackets are not shown when you edit the site. The language switch already works, but you see the words only in that language you call the site to edit. Without seo mode your modification in the xlanguage module works like a charme, thanks Michael!
Only for note, i will open another thread, the same problem we have with the pagebreak tag in the brackets. Without seo mode works, with wrapper it works not (the content module did not work with the pagebreak).