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