I used to use it for cockpit awareness at work. I really like it. I haven't played with topo info on it since I retired, but at some point will do so for fishing spots and the like.
Google didn't like Orux (and others) downloading their files and did some kind of legal "cease and desist" that required Orux to change their desktop application so you couldn't save Gearth files to offline maps. The older version of the desktop software still let me download Google Earth files to the device (versus live connection). I'm sure I still have that installer somewhere in my archived work files. I'll poke around and if I find it, shoot you a Google Drive link to the exe.
Sorry, don't know about Japanese, but the Orux developer is very approachable, so you could always shoot him an email.