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