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