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