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