Like in all fantasy and sci-fi fiction out there. It's either a universal language, magic or technology, like the universal translator. Like with all sandbox like settings, in MGE as well a lot of things are left for the Reader/Self insertionist to fill the blanks and make those for themselves. So either you want a story that have a stranger stranded there alone and have to learn everything from zero, language included or the old ROB'd into the world with speaking the native language/s and knowing the world's history and other meta stuff.
I believe there are more languages un the MGE world as we saw there are several types of writing (Zipanguan, runes...) , but it isn't confirmed so it's 50:50. Could be different writing but same language, although that's unlikely.