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