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