The Germans definitely have no post-war HT's (that I know of...yet).
They do have a rather basic MT line consisting of Leopards,
an interesting line of Leopard proposals (Borgward Leopard is a very good-looking tank, and is probably one of the best hull-downers in WoT)
but they have a rather rich and diverse LT line; whatever it is they lost in HT's post-war, they still retained their tendency to produce a light tank from any recon / APC / IFV / whatever.
As for the Japanese, though a lot of military documentation on the O-I is lost, there's another source for the top-secret projects: the big corporations that made and designed them (zaibatsu). And while almost all of them shed their links to WWII during the occupation, their archives still contain a vast amount of history just waiting to be published; all it needs is someone to trawl through all the data. That's how we got the newer, 'more correct' O-I designs (that awkwardly made WG's in-game Japanese HT tech tree unhistorical in just a few years). And interestingly enough, research on these paid off: the IJA apparently had designs for an actual normal-HT-sized HT as well, side by side with development of the O-I superheavies.
I'm fierce and I'm feeling mighty,
I'm a golden girl, I'm an Aphrodite
