Looks good. I kinda liked the idea of separating languages by categories but honestly that simply wasn't feasible.
Question. How is this handled in different locales? Will the types be in the English placement, or in the localized one?
By removing the "source file" suffix you avoided most of the trouble this could cause (e.g. in Spanish nearly all languages are called "Archivo de fuente <type>" or "Archivo <type>", and they'd all be filed under A), but there are still a few localized names (e.g. "Cascading Stylesheet" = "Hoja de estilo en cascada"). Probably the most reasonable approach is to not translate the names, and to use "short names" (e.g. "CSS" rather than "Cascading Stylesheet") in all locales.