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