Comment from Paulo summarizes well the Perl vs Prolog issue:
Perl developers fucked up big time by overtaking a file extension, .pl, used by Prolog, language that was already 15 years old by that time Perl appeared.
Linguist, the software that classifies source files had built-in measures (example files) to recognize Prolog .pl files. These were all removed by this commit with a rather shitty commit message: "Remove prolog samples for now and rely on .prolog extension". This does not work.
My repos that are all incorrectly classified: