In many ways it's much worse than the difference between English and French. If you are fluent in both of those languages, you can read a book that's written with some paragraphs English and some French. Software written in two different languages can't be combined nearly so easily.
> Software written in two different languages can't be combined nearly so easily.
As far as a human reader goes, I don't see why not. In fact, Objective-C and Objective-C++ provide practical examples of how dissimilar languages can be intertwined without detriment to the reader. To add to that, when writing pseudocode, people often do mix metaphors from multiple languages.
Granted, having a machine understand that kind of code to be able to do something with it is more of a challenge without a strict set of rules, but that's a completely different matter.
