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