If we are talking about the so-called. NPAPI plug-ins or its derivatives - on any. The condition is the ability to create a dynamically loadable library (.dll / .so) that implements and exports a number of functions with a specific API .
In practice, C is most often used as the most used to developers.
More often than not, it seems more rational to write an extension than a plugin. A plugin is needed if you need something rather specific, such as video encoding, or working with computer devices.