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