Tip for Boosters!
this is not a solution for the achievement, but for what comes after... (don't hate me for it, it's just to help)
If you managed to get it with the help of the Language-Trick, you'll probably have noticed that the name and description of the achievement is not English (or whatever).
To solve this you need to do the following for pre-NXE:
1. Go to the Xbox-dashboard
2. Navigate to the "Marketplace" blade
3. Press "X" to Sign Out, confirm it with Yes
4. Go to "Recover Account"
5. Enter your Gamertag and Continue
6. Put in your NET password and ID and continue
7. Wait for it to recover and check your English Achievements
1. Go to the Xbox-Dashboard
2. Press the Xbox-guide button
3. Press "X" to Sign Out, confirm with "Yes, sign out"
4. Click the "Recover Gamertag" button, and again.
5. Confirm to exit your current session with "Yes"
6. Enter your Gamertag and Continue
7. Enter your Live ID and your password and Sign In
9. Wait until your profile is downloaded and check your English Achievements
The solution is not invented by me, although I wrote down the NXE version with the help of the following webpage: http://www.myxboxspot.com/forums/halo-3-glitches/1387-how-ch...
The pre-NXE solution is a retyped and shortened version of the idea that can be found on the same webpage, I have copied it because I wanted to spread the word about this solution.