how do I assign roles, I mean i put as secondary storylines a stereo audio track in one language and a surround audio track in other language but when i export i got all of them mixed, in bot audio tracks available in the file
The Roles can be set and changed in FCPX. Select the seperated audio clip and show the Inspector (⌘4). Go to the Info tab and Roles will be the first dropdown. You can create custom roles if you want too.