Click on "browse by category", click on a link to a category that best fits your
search purposes, and then click on "filters". In the drop-down menus that since
appeared, select "require", "programming language" and then select the programming
language you want to search for.
Yes, it'st a UI nightmare, it's non-intuitive and it's a pain to deal with. That's
sourceforge's user interface.
Rui Maciel