You can go into Usenet archives, and ads on digital copies from Byte, Computer Shopper, Dr. Dobbs, PC Techniques, The C Users Journal, The C/C++ Users Journal, Your Sinclair, Amiga Format, MicroHobby, Micromania, SoloProgamadores, Spooler,...
And see which compiler toolchains had more ads, articles submissions, or source code listings.
No, this is silly. You can look at the availability and maturity of toolchains, the rate of release of projects written in that language, the rate of release of books and learning materials, the rate at which universities begin teaching the language, the volume of discourse devoted to that language in magazines and the online venues which did exist (e.g. Usenet), and crucially the declining metrics of all of the above for the direct competitors of that language.
And see which compiler toolchains had more ads, articles submissions, or source code listings.