Even in English, there's crossover there. I mean, should the phrase "of course" literally mean what we use it for? I'm pretty sure it's a shortened form of "it's a matter of course," meaning that the course of logic inevitably leads to some obvious conclusion. But the same phrase is also often used to mean "by the way" in colloquial speech; it's a conversational segue that refers to the same "course of logic," which in this case will lead the discussion into a natural transition. Similar to the way indeed is used, or in olden days, verily.
For more examples of this kind of phrasal crossover in slang, see duh and eh. ;-)