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