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