How do I export .MP4 with multiple language audio tracks?

Choose Windows>Show Movie Properties. Use the Enable checkboxes to select or deselect the tracks to play. Note that tracks must be enabled to be retained when exporting a movie in Pro, according to the QT 7 users guide. That seems to be a change from QT 6, which I use. In any case, here is a link to the user guide for QT 7:
http://images.apple.com/quicktime/pdf/QuickTime7UserGuide.pdf

You may be right about the limitations regarding audio tracks in .mp4 files. The guide I quoted from and linked earlier doesn't provide such info on .mp4 files. You probably need to search the web for such info about .mp4 files.
One thing I do note that isn't clear in the guide is that when I Export a movie with more than one enabled audio track they are mixed down to a single track that plays both of the former separate tracks simultaneously if they overlapped in time in the original movie. This happens whether I export to a new . mov file or some other format like avi. That leaves unanswered whether those other formats like avi or mp4 can have more than one audio track You apparently can't Export multiple audio tracks from QT but you can "Save" muliple audio tracks in .mov files.

When the file gets played back, only audio track 1 is heard; choosing English from the Choose Language menu doesn't activate the English audio track.
What am I doing wrong?

Was intrigued by the topic and decided to attempt a test of my own. Not knowing anything about the subject, checked the help file only to discover that it is somewhat less than helpful. Tried creating a multi-language files based on how I might expect QT Pro processing to operate. Han no problem merging two 2 MP4/AAC files into a single video track/2 language track vdeo which I then saved in a MOV container. This was the result. You can open the URL directly to QT Player but I was disappointed that there does not seem to be an ability to choose an alternate language during browser playback. (May request this as a new feature.)

Based on my limited experience wondered if the problem my be in one of two areas:

1) Know nothing about the M4P format but from the description assumed it might be a protected audio format. Since I had no problems using AAC audio in my test, wondered it this might be your problem.

2) Since you did not describe the specific workflow used, I wondered if you had failed to create the complete language menu loop which does apprear to be madatory but less than totally intuitive.

Seem to work here too...looks like you may be able to do this to video tracks too...Dr. Who, my head hurts now.

g-4 1.2 gig Mac OS X (10.4.7) Quicktime 7.1.1-1.5 gigs of ram, 2-21" Sony monitors

Seem to work here too...looks like you may be able to do this to video tracks too...Dr. Who, my head hurts now.

Yupper! Already done that. You can key on multiple or independent audio, video, audio and video track combinations based on the language selection. Don't know if I would use it but it implies your can use alternate angles, languages, commentaries, mono, stereo, etc. combinations if you have a mind to do so. Too bad the iPod can't handle them.

But back to my basic question: How does one export dual audio in MP4 format using QT Pro? I don't think it's possible, because the resulting file always plays both tracks simultaneously (using Export... Movie to MPEG4)

I'm not sure I understand your question. The format is MPEG-4/AAC/AAC. Yes the file container is ".mov", but if all you want is an ".mp4" file extension, then change it manually.

Basically, You can't have multiple AAC tracks in a saved ".mp4" container. You can, however, "Save" them in a ".mov" file container. Therefore, the "Choose Language" option only works with this file container (as far as the QT Player is concerned). If you try to "Save" multiple AAC tracks in a modified ".mp4" container, it will automatically switch to the "Save As..." option with a ".mov" container. If you attempt to export multiple AAC tracks using the "Movie to MPEG-4" option and "Pass Through" the audio, only the first/primary track will be audible. If you use the "Movie to MPEG-4" export option with mono and/or stereo audio without passing through the audio, then you will end up with a single "blended" AAC audio track. On the other hand, if you pre-assign your language audio tracks to non-conflicting channels, you will end up with "languages" on different audio channels. Since the "Choose Language" option is non-functional with a single AAC track file, you would then have to manually re-assign the wanted/unwanted audio channels in the "Properties" window each time you wanted to switch listening options.

However, if you open that file you created in a popular player, such as VLC, you'll notice that the audio track labels are screwed up. You won't see "English" and "French", rather you'll see:
Track 1
Track 2 - [''a]

The label designation is a part of the media player -- not a part of the media file itself. Apple uses "language" references since these entries are also supposed to be "tied" into the default language set by the platform user. VLC uses a more generic reference probably assuming a more general use in conjunction with audio formatting. (E.g., stereo (L/R) vs AC3 5.1 audio option in the same file.) If this bothers you, request the feature be changed.

I got this from another post I remember a few months back. And this may be why your having problems with the audio track or partly:

<.............."MPEG-4 Part 2 is an international standard and does not belong to Apple.
(the same goes for H.264)
It never has supported any audio beyond stereo no matter what platform.
It's not part of the spec for this format."...........>

The audio support for MP4 is limited, container. It's the MP4 container that's limiting you from doing what you want to do. And it's the mov comtainer that allows this.............I think...