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