How hard is German for an English speaker?

English English sounds weird. Let's call it British English or Metropolitan English better.

The problem with the name "British English" is that the adjective "British" applies to the entire UK or at least the island of Great Britain, which also includes Wales, Scotland, and Cornwall (which is distinct from the rest of England) along with England proper. "English English" is more specific in that it clearly refers solely to the English of England itself, and not Scottish English or Welsh English. As for "Metropolitan English", the problem with it is simply that it would be hard for the average reader reading such to know what it is really supposed to mean.