Honestly, I think everyone is lying about their numbers except the western world (Europe, Canada, etc.). In the case of the US - it's just ignorance of not doing enough testing to accurately have our numbers.
But India, China, Japan, Russia, and all of LATAM? I think they are all full of shit.
I think everyone is either lying or just isn't able to test sufficiently, except for South Korea. I doubt it's just (well, not entirely) deliberate propaganda in the case of the poorer countries, they just don't have the ability to test for the virus.
If Italy's figures are accurate, for example, it means the fatality rate of the virus there is approaching 10%. Seems much more likely (and slightly less scary) to assume that they are just substantially undercounting the infected. Not necessarily for want of trying.
The UK authorities admitted that the real figure is probably ten times the recorded one (not completely a guess - based on extrapolation from samples where the exact figures were known). For countries like Brazil or Turkey it's probably both an inability to test plus national pride not wanting to admit the scale of the problem. For other countries it might lean to more one or other of those.
South Korea appears to be the only place that has decided that to fight it they need good numbers, and national pride be damned.