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