I have decided to make an academic transition from Electrical and Electronics Engineering into Mathematics after graduation. Although my first degree is from an Asian country it is a well accredited one. Japan is at the top of my list of countries where I wish to do my graduate-level studies. I'm particularly interested in doing a Master's program taught entirely in English and I see some National universities in Japan are conducting such courses under the G30 program (There might be other programmes as well).
But I have concerns regarding language being a barrier, as well as the rigour of the curriculum I will be studying there. My goal in the near future as of now is to get a good postdoc position.
In general, how would graduate studies in Japan differ from those in the US, specifically for mathematics?
Note: I've deleted my previous ambiguous question. Thank you @LoneAcademic for the suggested edits.