Edit: As of 4/26, this achievement will be much easier. You don't have to enter the top 250 of average or total score (all time) anymore. New leaderboards are included and the achievement will unlock if you will place in the top 250 of any of these leaderboards. These are:
Total score (today), (this week), (this month) and (this year)
Average score (this week), (this month), (this year) and (this month)
High score (this year)
Most words (this month) and (this year)
Players who got this in the WP version of wordament will also achieve this in Win8 by starting the windows 8 version of wordament. (works the other way around as well. )
You get this by either placing in the top 250 of the average score leaderboard or in the total score leaderboard. To enter the total score leaderboard you must have at least 250,000 points.
To enter the average score leaderboard you must have played 100 games and have at least 85,000 points. If it doesn't unlock at 85,000 points you can send in game an email to the developers and they will fix it for you. (thanks to Tully123, Zalexzy and C4B0S3 for pointing out.)
It is very hard to get it in English, or in your own language, like Dutch for me, but there are some ways to get it easier. You can use a wordament solver to solve the puzzle for you but you can get banned for this.
Recently a few new languages have been introduced. In Arabic only 2-15 players play the game at a time. I got my achievement this way. I every time just guess for 3-letter words. In a digram round just go and guess all the possibilities with the diagram. Try and do 2 tiles first, and afterwards the Tile - Digram Tile - Tile, T - T - DT and the DT - T - T. After a while you will recognise certain letters which are often used after each other. One I found very useful myself is when you have a round with a symbol which looks like a degree sign and gives you ten points for using it. Once you have an I symbol next to it try every possibility with I - degree sign.
I hope this helps.