Test an already existing hypothesis but in a different setting/country?

I think you have a big misconception of what plagiarism is. Passing other people's work as your own is plagiarism; doing something and later discover that it was done before is not. It is not even unethical.

The worst case is that your work is rendered redundant, but this depends on how different your settings and results are.

If you want to present science as new, it has to be new. If the setting is sufficiently different, then you can present it as new, but you still need to cite the research that took part in other countries.

For example, if there has been research in the relation between air quality and chocolate consumption in Canada, nothing stops you from performing the same research in India. But you should still cite the Canadian team.

Plagiarism is when you present work as your own, whereas in reality you took it from somewhere else. If you inadvertently repeat research that has been carried out before, your work may be rejected for publication for not citing previous work properly, but it's not plagiarism.

If testing the same hypothesis again is plagiarism, then the reproducible science folks are in trouble.

You seem to have a very flawed notion of what plagiarism is - it's the wholesale copying of writing without attributing it to a source. What it isn't is performing the same experiment in a different setting.

Not only can you continue, but you should. Testing the same hypothesis in a different population helps to uncover the variability of the effect, its generalizability, etc. Testing the same hypothesis in different settings is good research. In some fields, this is even recognized as important enough that "Someone else did this elsewhere" isn't even particularly grounds to consider your work not important.