Indeed, I don't think the mapper has anything to do with internationalization. It certainly can't be used to get a decent German keyboard. The keymap code in 0.65 and above is meant for that, exactly like DOS worked.

The mapper is more a piece of code that ensures that you can access all keys on every platform, even though your particular platform may not even have the usual set of keys (think of F-keys and all that).

Okay - I stand corrected 😀

I don't even know what "rewrite the mapper" means and what to do with
keyboard.cpp. Could you explain in a more... formal language?

Don't bother, they're just talking about how easy it is (in their opinion).
In fact it is not possible with the current layout of the dos input handling of dosbox.

...so do I have any way of doing it that doesn't require learning tomes of programming or do I have to turn to another DOS emulator that supports the simple task of ctrl+break, or wait a few eons until a patch/mod is made to fix this?

Of all the keys it just HAD to be Break...

Use another emulator.
Qemu/VirtualBox/Bochs for GPL software
VPC 2007/Vmware Server/Vmware Player for free software

that supports the simple task of ctrl+break

Closed. Wait eons or something.