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