Never having needed to do this, I'm pretty certain that MEP does NOT allow multiple language audio tracks but VPX does. So, if you wish to create a multi-language DVD, with optional audio tracks, I think an upgrade to VPX may be your only option.
. . . . does MEPP support multi-channel audio on video output . . .
Unfotunately not, for this you would need Video Pro X.
. . . . like having a english and a german track . . . .
For this I used to make dual movie discs, ie I copy and paste the first timeline into a second, then change the titles and audio track to German. MEPP takes care of the disc menu automatically.
The disadvantage with this is that the individual timeline movie can only be ~ 1 hour long maximum to fit on a standard DVD or BD disc.
hm, then I think I'll better would encode the videos similar to you but then use another authoring software for the DVD menu and use some avimux or ffmpeg tool to extract the audio track from one movie and interweave it into the second one.
the Johnebaker solution is the easier and cheaper solution also replace the dvd or BR with a USB key and copy two distinct movie. But the best solution more work is a real DVD Authoring solution you have access language choice track and caption. More work but better result.
As indicated, you would need VPX to have the option to switch languages on a DVD. With this, you get a second (or third, or fourth) audio file on the DVD for the other language. The video is not repeated. Using John EB's method, you end up with two video files, one with language 1 text, the other with language 2 text, and two audio corresponding audio files, thus limiting the length on a DVD/BR.re
The titles are embedded in the video and are not separate, which is why you end up with two files.
If you only want titles in one language and you are not burning to a DVD/BR but only want individual mp4 files, then put language 1 commentary on one track, language 2 commentary on the second track. When you export to mp4 (or another format), mute the language track that you don't want.