I'm (after a hiatus of some 30 years) dabbling again in Modula 2 (yes, too much time cooped up). But neither ELPA nor MELPA knows anything about a mode for GNU Emacs. This site seems not to mention the language either. Any hints? Perhaps (ab)use a mode for a similar language, like Pascal?
To my surprise, after looking all over without getting any leads (and thus asking here), I just set to edit some Modula 2 source code. I was prepared to use plain text mode or a mode for say Pascal (somewhat similar). To my surprise, emacs went into Modula 2 mode.
So the short answer is: Modula 2 mode is build into the standard distribution.