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