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