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