I'm not sure where you get that language statistic from. I'm going to assume whatever tool you're using thinks that "JSON" and "YAML" are languages, to which I respond that they're not or at least not as significantly so as a programming language with its own paradigms, libs and tools. The repo in question is mostly C/C++ with a relatively small amount of other stuff to provide tooling support, and the languages used for that are really not all that problematic, difficult to understand, or unsupported.

As far as LOC goes, I know well enough that it's a meaningless statistic that has very little practical use. I've written 34 lines of JavaScript that were as meaningful as 25k lines of C, but those lines of JS were obviously interpreted on an engine that's millions of LOC.