Screen Credit Card Processors By Gateway

If you need to do numerical analysis in a scripting language, you pick python because it has numpy.

I once had to make a QR Code reader and writer back when it was only seen in Japan and the only library available was for Java, so I picked that.

Recently I had some ruby code that parsed a file, but I needed to pump it into a proprietary database with only a JDBC connection... so I picked JRuby.

Often picking a new language is much easier than rewriting a particular library.