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