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