I would put all the audio tracks and the video track in one file, if possible. I use the MP4Box utility to do this (not part of Wowza, but one should be able to find it easily enough) -- the command could be something like this:
Then specify the audio track to use when calling the Wowza video URL as specified here:
mp4box -add video.mp4 -add english.mp4:lang=eng:group=1:name="English Audio Track" -add french.mp4:lang=fre:group=1:disable:name="French Audio Track" -new new.m4v
You will have to reload the page/video if you want to switch audio tracks while streaming, but otherwise this works great across all formats (RTMP, HLS for iOS, etc.). And it makes local playback nicer too, if that's part of your workflow -- iTunes and other players will let you switch languages/tracks nicely.