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The monthly salary/income question for the B category visas is asking for your monthly income in your local currency. So whatever currency you receive with your paycheck is what they want to know. Obviously you wont be paid in their currency, since you are visiting to only get a visa. They could potentially ask you for a paycheck stub receipt to see if it matches. Good luck!
Also, it's perfectly normal to get B2 visas as a non-resident in a 3rd country. You simply have to contact the consulate/embassy and make sure they allow it. Half of them do, half of them do not. It is usually due to staffing and language support.
Changing the country for a US visa interview happens quite a bit, throughout the world for various reasons. For instance, my Russian in-laws waited a year in the Moscow queue only to have their B visa interviews cancelled, and the state department kept the money!! We had to repay and wait another year to have their B2 appointments in Budapest, in which they were granted US tourist visas. They have already been here with us in the US for 6 months and are going home this weekend. I hope it works out for you.