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