Here is the full list of all 30 The Legend of Korra achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Got 10 Knockouts in Pro-bending matches.
Completed Chapter 8.
Collected 10 cabbages.
Spirit-bended 200 dark spirits.
Went into Avatar State 10 times.
Maxed out all bending types.
Completed a Naga Running sequence without hitting anything.
Completed all tutorials.
Completed Chapter 7.
Performed 100 Finishing Moves.
Obtained all combos.
Dodged 100 times.
Went into Clash Mode 10 times.
Countered 100 times.
Completed Chapter 6.
Completed Chapter 5.
Completed Chapter 4.
Completed Chapter 3.
Used your first equipped item.
Jumped 100 times.
Entered the Collection Screen for the first time after finding a treasure.
Equip your first item in Korra's Room.
Bought your first item at the shop.
Completed Chapter 2.
Completed Chapter 1.
Completed the game on Extreme difficulty.
Purchased 12 talismans.
Collected every treasure item.
Won a Face-Off in a Pro-bending match.
Completed the highest difficulty of Pro-bending.