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