Surely, nobody would bring a #minitel at #39c3 near the house of tea for public use. That seem very unlikely
Rumors also than there won't be someone around for explaining what it was and how to interact with it, day 3 from 14h30 to 16h and from 18h30 to 20h.
Or maybe even this night from ~2h. Surely the person that did not put this minitel here would be sleeping

Update : some keys of the keyboard have stopped working during the night.

It is still possible to use it despite that, as long as you don't need to type the letters s, d, f or g or the numbers 1, 4 or 7.

Unfortunately, while the fact there is entire rows disabled give clues on what might be wrong (the main suspect being the ribbon cable connecting the keyboard), the chances of it being repaired during the last hours of Congress are pretty low.