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
Acquire all available upgrades
Find all the postcards
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
Pull the lever on the underground level
Bullseye!
Collect 9999 helmets
Beat 2500 Romans
Buy a figurine
Beat 30 Romans in Fury mode
Free Kerosene
Find all the diamond helmets on a level
Gain access to LuckSore
Finish a challenge at Gold rank
Stun 10 Romans at once
Beat 100 Romans under the effect of a magic potion
Free Battermix
Gain access to Venitia
Obtain x6 multiplier
Buy an upgrade
Enter Las Vegum