This likely has a lot to do with how they do detection. Swift uses the .swift extension, which is pretty unique, so detection is as simple as checking for the

This likely has a lot to do with how they do detection. Swift uses the .swift extension, which is pretty unique, so detection is as simple as checking for the file extension with a very low risk of a bad classification. Some of the older, more popular languages uses more common file-suffixes, which may be shared between multiple programming languages, which has a negative impact on classification accuracy.