Here is the full list of all 10 Wordament achievements worth 50 gamerscore. It takes around 1-2 hours to unlock all of the achievements on iOS.
You found a theme word
You beat all your Frenemies in a round
You've played Wordament in more than 1 language
Found the longest possible word in a round
Completed 10 rounds
You found a digram word
Completed 100 rounds
You used rotate to find more words
You played a game where you used all 16 tiles to make words
Place better than 50% of the players in a round