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