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