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