This one is easy. So, most phones only have roboto. that's why most apps only overwrite it. If you want to change one, just rename it.. but if you want to ADD one, you have to add a line in a config file.
I have a bunch of Korean lgworld fonts (they all support English characters) that worked for me, but they're paid and I'm not allowed to post. But you could very well just Google it. "Lgworld fonts"