Here is the full list of all 19 My Life: Riding Stables 3 achievements.
Unlock all outfits
Complete all tournaments with a gold medal
Complete all tournaments
Own every breed of horse
Reach tournament rank 5
Play all minigames
Maximize all stats of a horse
Reach tournament rank 4
Rebuild the riding stable
Unlock the lunging yard
Unlock the therapy center
Gather all collectibles
Reach tournament rank 3
Unlock all areas
Unlock a new area
Sell a horse
Buy a horse
Reach tournament rank 2
First tournament completed