Here is the full list of all 52 Letter Quest: Grimm's Journey achievements. It takes around 10-12 hours to unlock all of the achievements on Windows.
Earn 120 stars
Earn 99 stars
Spell 2000 words
Purchase 50 merchant items in battle
Do 100 critical attacks
Fail to open 20 treasure chests
Purchase 30 upgrades
Spell 200 double-letter words (ex: 'bubble')
Purchase 10 potions
Use 2500 vowels
Defeat 250 monsters
Dodge 50 attacks
Complete 50 quests
Spend 25000 gems
Bust apart 100 gem piles.
Defeat 5 monsters with exact damage
Fill the entire board with plague tiles
Use 5000 letters
Fill the entire board with duplicator tiles
Purchase 5 books
Open 10 treasure chests
Use 100 crystals
Reach max level with one book
Earn 15000 gems
Earn 29 stars
Deal 25000 damage
Beat a stage with only 1 health remaining
Spell 50 six-letter words
Earn 1000 book XP
Spell 25 palindromes
Spell a word that contains two 'Y's
Use 25 plague tiles
Spell the word BANDITS
Use 500 corner letters
Swap all letters 50 times
Take 10000 damage
Lose from taking tile damage
Spell 3 words with no vowels
Spell 10 seven-letter words
Use 500 letters from the top row
Spell the word BACON
Deal 10000 damage
Spell 5 eight-letter words
Use an entire row in one word 3 times
Spell a word containing two or more crystals
Finish a stage with full health
Open a treasure chest with no incorrect guesses
Spell a word that does zero damage
Leave a monster with only one health
Spell 3000 words
Earn 20 crystal stars
Earn 40 crystal stars