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