If I know a certain concept X requires 12 seconds of speech to express in English, and I don't know anything about Swahili beyond the fact that it's a human language, my first guess will be that concept X requires 12 seconds of speech to express in Swahili.

You'd be very wrong for a lot of technical language, unless they just imported the English words whole sale. For example, "Algorithmic Information Theory," expresses a concept well but I'm guessing it would be hard to explain in Swahili.

Even given that, you can expect the languages of humans to all have roughly the same length because they are generated by the roughly the same hardware and have roughly the same concerns. E.g. things to do with humans.

To give a more realistic translation problem, how long would you expect it to take to express/explain any random English in C code or vice versa?