Depending on your definition of simple you could use tsmuxer and eliminate all but the dub you want. It doesn’t re encode anything so it only takes a few minutes to save the new file and it’s pretty user friendly.
I don’t think it will save as an mkv though, I think it only does .m2ts so you might have to then open it in something like avidemux and resave it as an mkv if your tv won’t take that format.
Just use MKVmerge instead of tsmuxer, and do basically the exact same thing.
Yep. MKVmerge (aka MKVtoolnix) is exactly what you want here.