Here is the full list of all 30 Asterix & Obelix XXL 2 achievements. It takes around 8-10 hours to unlock all of the achievements on Windows.
Find all the postcards
Reach 100% completion
Find all the diamond helmets
Finish all challenges at Gold rank
Buy all the figurines
Beat every type of Roman
Collect 9999 helmets
Beat 2500 Romans
Finish a challenge at Gold rank
Acquire all available upgrades
Stop Caesar's invasion plan
Beat the Caesars
Free Suchafuss
Open the door on Pirate Island
Find out who Getafix really is
Find all the diamond helmets on a level
Discover the fake Gaulish village
Beat 30 Romans in Fury mode
Stun 10 Romans at once
Pull the lever on the underground level
Free Kerosene
Bullseye!
Gain access to LuckSore
Free Battermix
Beat 100 Romans under the effect of a magic potion
Obtain x6 multiplier
Gain access to Venitia
Buy a figurine
Buy an upgrade
Enter Las Vegum