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