Go to your Dashboard. Change your language to the second option from the bottom. 
Start Halo 3. Invite four other friends that are about the same rank as you. Also 
have them change their language to the same one as you. Get everyone in the same 
party before you want to get them in the same party. Everyone must search at the
same time. Everyone then must make a game in Lone Wolves. Before you go to start 
the countdown, press X to change the search options to the bottom one, which is 
to search for the same language. If done correctly, chances are you will be in 
the same ranked Lone Wolves game as your friends. You can now get achievements 
or level someone up.