What you need to do is to play a lot of Snap Attack games, to get a total of
50'000 points.
Your progress is shown under the
Rank & Stats menu.
The points from other languages count as well, so don't be afraid to try that!
Some tips:To get more points every round, try to add endings to words in that level. CALM + ER and DOSER + S.
For easy 100-150 points each round, move vocals around fast to get quick points. (A, E, I, O are the most common)
Use
http://www.wordfeud-helper.com to find long words, by putting in your letters in the start of the round.
Good luck!
Edit: Added some tips