Here is the full list of all 20 Doodle Tanks achievements.
All light tanks created
All USSR elements unlocked
Unlocked Panther, Tiger I, Tiger II
Bölter created
All TDs created
Unlocked the Pz III and Pz IV tanks
Unlocked all Germany events
Unlocked the PaK 44 L/55 and KwK 44 L/38 guns
Maus created
Unlocked all elements of Germany
First tank created
8 groups created
All Lend-Lease supplied tanks unlocked
25 elements unlocked
T-34 unlocked
50 elements unlocked
All T-34 unlocked
All inventions created
T-34, KV-2, IS-4 tanks unlocked
All medium tanks created