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