As others have said this is not the way to go about making a dual language programme.
There are two elements, the narration and the interviews.
The narration must be translated by a professional who can translate to time, ie so that the foreign language narration fits the inage edit. Inevitably this may involve some compromise but if the writer’s a pro it should work.
The interviews can be transcribed and translated to time as the narration or subtitled. The choice will depend on the acceptability of subtitling to the audience and budget eg English-speaking audiences are relatively unused to subtitles, whilst French audiences have got used to subtitles since so much of the material they see originates elsewhere.
Having said that the majority of films that reach the cinemas in France these days are overdubbed in French.
Finally, if the programme is to genuinely appear to have been made for the foreign language audience there should be budget to re-edit the images to suit a translation to “quality” (ie without compromise) not to time.