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