You have a source for Gothic being Mandarin-descended? Never heard that before, but I could see it. The imperial palace being in the himalayas would certainly put it geographically in the correct place, but I don’t remember from where he started the unification wars.
I think it’s something from an old Rogue Trader article? So it may be more a metacommentary from an old writer sort of thing, that Gothic would have been descended from Mandarin with a bunch of English vocabulary mixed in, albeit all unrecognizable after tens of thousands of years of sound changes.
Just checked and Lexicanum has the following sentence on Low Gothic:
Low Gothic is a bastardised version of High Gothic, combining additional elements from several of the oriental languages of ancient Terra.
So close enough, but it still had to hit the 80’s racism quotient lol.