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