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