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