user3355: Is it possible to upload one video on YouTube, and have multiple soundtracks for it? Much like one can choose the subtitles, can one make several language-specific voice-overs for the same, say, screen-cast?
If that feature is not present on YouTube, are there calls or plans for it? What other services may have this implemented?

user6166: As of now, Youtube doesn't allow multiple soundtracks other than adding a music-track.  So you'll need to create multiple videos with voice-over for different languages. Thankfully however this is already automated using a bash script.  
Demo Video with Automatic voice-over translation from SRT subtitles using eSpeak
VoiceOver Script Version 0.3 to convert Subtitle file to Audio Track using eSpeak 
This solution works on Linux but I guess one can use Ubuntu Linux as a VM using virtualbox on windows.

user-1: When uploading to YouTube: no (for now...)
Your audio needs to be premixed into one stereo (or mono) channel.
When using YouTube's online video editor: yes, but you are limited to voice-over and music tracks
For more info:
http://support.google.com/youtube/bin/answer.py?hl=en&answer=183851
(see point 4. adding audio)

3355: <p>Is it possible to upload one video on YouTube, and have multiple soundtracks for it? Much like one can choose the subtitles, can one make several language-specific voice-overs for the same, say, screen-cast?</p>

<p>If that feature is not present on YouTube, are there calls or plans for it? What other services may have this implemented?</p>
 6166: <p>As of now, Youtube doesn't allow multiple soundtracks other than adding a music-track.  So you'll need to create multiple videos with voice-over for different languages. Thankfully however this is already automated using a bash script.  </p>

<p><a href="https://www.youtube.com/watch?v=ud38LEKKY6k" rel="nofollow">Demo Video with Automatic voice-over translation from SRT subtitles using eSpeak</a><br>
<a href="http://www.particio.com/downloads/voiceover-0.3" rel="nofollow">VoiceOver Script Version 0.3 to convert Subtitle file to Audio Track using eSpeak</a>  </p>

<p>This solution works on Linux but I guess one can use Ubuntu Linux as a VM using virtualbox on windows.</p>
 -1: <p>When uploading to YouTube: no (for now...)<br>
Your audio needs to be premixed into one stereo (or mono) channel.</p>

<p>When using YouTube's online video editor: yes, but you are limited to voice-over and music tracks</p>

<p>For more info:
<a href="http://support.google.com/youtube/bin/answer.py?hl=en&amp;answer=183851" rel="noreferrer">http://support.google.com/youtube/bin/answer.py?hl=en&amp;answer=183851</a><br>
(see point 4. adding audio)</p>
