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.
Come to think of it you can technically do all of it in avidemux but I have always had problems getting it to do anything, it always says it’s going to do something then inexplicably doesn’t do it, so I don’t recommend using avidemux for anything other than simple encoding, or in this case remuxing.