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