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