Here is the full list of all 14 Transformice achievements. It takes around 200 hours to unlock all of the achievements on Windows.
Bring back the cheese first once
Buy 20 hats in the shop
Buy 10 hats in the shop
Buy 2 hats in the shop
Save 100 mice as a Shaman
Get 1 cheese
Get 300 cheese
Get 1000 cheese
Get 9001 cheese
Save 2000 mice as a Shaman
Save 10 000 mice as a Shaman
Bring back the cheese first 10 times
Bring back the cheese first 100 times
Bring back the cheese first 500 times