Components of KDE are largely licensed under the LGPL, and many of them represent libraries written in C++. It uses the popular Qt graphics library. Where the competing GNOME project tries to be fairly language-neutral, with library bindings available in many languages KDE is largely biased towards C++.
Flamewars between proponents (usually not programmers) of GNOME and KDE have commonly erupted, not dissimilarly to controversies over the relative merits of Common Lisp and Scheme.