I actually had tremendous fun pushing several language to the 15 puzzle achievement.
Most of those language were unknown to me and it was really great experience with loads of fun.
The level of difficulty of the puzzle increasing slowly, it allowed me to get a progressive grasp.
However now, there is no more achievement ahead and it’s not as much fun doing puzzles in other languages when you know that won’t get anything out of it, aside from improving your programming knowledge obviously
I believe that with some higher per language achievements, it would provide a lot of challenge and fun. As completing more puzzle in a language requires you to complete even more difficult puzzles.