@casey-jones no its sadly not, most of europe uses the same gauge atleast (except for parts of the iberian peninsula and some specialized railways) but overhead wire spacing, current and safety/signaling systems can be very different. Also not every train is licensed to run in every country. The new railjet gen 2 cab cars from siemens are allowed to run facing forwards in Germany and Austria, but not yet in Italy, where they can only run at the end of a train or behind a locomotive (defeating the whole point of a cab car)

Most trains can run in multiple countries, but afaik never everywhere, and its usually pretty complicated