> You would have to make the rounds yourself informing the governments concerned you renounced their respective citizenship.
The Japanese government requires that you have renounced your other citizenship(s) as a condition for acquiring Japanese citizenship [1, item 5, in Japanese]. I know a number of people who have taken Japanese citizenship, and they all had to go through a formal citizenship-renouncing process at the embassies of their previous countries of citizenship.
Exceptions seem to be made only in cases in which the applicant, for some reason, cannot renounce a previous citizenship.