Keyboard typing in random characters

That can be keyboard debris, or a keyboard failure, or can be caused by a battery that is swelling.

Debris is much less likely here, given your problem description and the testing you have already performed.

This probably won’t help: How to clean the keyboard of your MacBook or MacBook Pro - Apple Support

What probably will help: bring it into an Apple Store or an Apple authorized service provider for a look and for some diagnostics.

If this is the battery swelling, bringing it in sooner is better than later. When swelling progresses—again, assuming this is due to battery swelling—you can sometimes see deformities and bulging occurring when sighting along the edges and surfaces of the MacBook Pro chassis.

If the keyboard has failed, this will probably involve either replacing the top case (the keyboard is part of a much larger assembly), maybe also the battery if that’s the trigger here, or replacing the whole MacBook Pro.

Have current and complete backups of your data, too.

bafluffia wrote:

Now all of my keys on my actual MacBook seem to type in foreign characters even though the language preferences are all clearly set to English.

This will happen if your option key gets stuck. asdfg become åß∂ƒ©