I live in Germany. 'Ja' here means 'ich stimme zu' only when explicitly asked. That's why Germans stick 'Ja?' after every second sentence. Ja? In general, 'ja-a...' means 'I hear you', same as almost everywhere else. That has been my experience.
And why do they say ‘right?’ every time? Because without it my ‘ja’ does not mean ‘yes, sir’, but rather ‘I hear you, go on’. So, same as everywhere else.
Not really, if you get a "yes" in the Netherlands, Nordics, Germany or Poland it does mean, simply, yes.
The consequence of which is that actually getting a "yes" takes a lot of work.
I don't dare speak for other countries, no experience there.