PHD: Same core idea but in context of different country?
The scientific significance of the work really depends on what the nature of the subject is and how much value is added by doing the additional research.  For two extremes, consider:


A study on the effect of GMO feed on pigs in Freedonia, using the same methodlogy as a just-completed study of the effect of GMO feed on pigs in the Duchy of Grand Fenwick: low value, because there is no reason to think pigs will react to the same food differently in two different places.
A study quantifying the size of difference economic sectors in Freedonia (which has not been previously/recently studied), using the same methodology as a just-completed study of the Duchy of Grand Fenwick: high value, because countries typically have different economies, and understanding a country's economy is very valuable for planning policy.


You can evaluate the value of your proposed contribution similarly, by asking how much there is expected to be a difference, and how much knowledge your study will add.  Your advisor can then help you further tune the scope for their expectation of an appropriate amount of work for your dissertation.