It's not a bad piece of rhetoric, I even use it from time to time. But it's only useful on programmers who haven't stepped much beyond their own narrow interest in technology--anyone who's done work across a variety of languages ought to realize that "can interface with C" isn't a feature that's supposed to be marketable, it's a hard requirement. They may have never had to do this themselves, but they should at least know in principle it can be done. In practice it's often a lot more difficult than it should be. If Python's C-interfacing capabilities were as slick as Clojure's Java interfacing ones, I wouldn't want to write about it.
What do I mean by "can interface with C"? A language that can interface with C is a language that can directly call functions in a compiled shared object that was written in C, and also where C can get at the language's internals as well to call its code and have interactions. This is distinct from using the other language to instruct the operating system to run a compiled C program and give it the results, and vice versa. Java interfaces with C, and Python interfaces with C.
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