I've used Subtitle Workshop in the past, in combination with an audio app that allows me to zoom into the waveform and see when lines of dialogue start and stop, but I'm not very efficient at it, it takes me forever so I don't do it often. In the case of BBF, the French dialogue is spoken a bit quickly, so you'd probably have to simplify the lines a little, while keeping the spirit of the original. Even in the English-dubbed trailer, there are dialog differences because of the timing issues.
I've used Subtitle Workshop in the past, in combination with an audio app that allows me to zoom into the waveform and see when lines of dialogue start and stop, but I'm not very efficient at it, it takes me forever so I don't do it often. In the case of BBF, the French dialogue is spoken a bit quickly, so you'd probably have to simplify the lines a little, while keeping the spirit of the original. Even in the English-dubbed trailer, there are dialog differences because of the timing issues.