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