new country

I've not done it, but one trick might be to use the UN post adjustment system - check http://icsc.un.org/resources/cold/par/class/archived/feb2015b.pdf

The post adjustment for Belgium is 41.2; for Paris, 48.0; for Geneva, 99.0.

So if you worked for the UN, you would find that if you earned 141.200 EUR in Brussels, you would earn 148.000 EUR in Paris or 199.000 EUR in Switzerland.

It's at least a rational basis for how one set of employers would adjust your salary based on location. BUT you also have to factor in that the benefits in different countries may be quite different (if you work for the UN the benefit package is consistent).

I'm not an expert at negotiating salaries by any means, so I wish you luck!