If we have an interest one interest item (per country), then the current input method is logical, you identify the source of the interest item.

If there are 2 and more interest items (per country) which is often the case, the this method appears to be unnatural, as you have to randomly pick a random item, or do it for all unnecessarily.

If there are 0 interest items, then you have to be creative to think that you can input details on an interest item that does not exist - it maybe helpful to put a label like "foreign interest" and maybe $1.

I think the current way is Okay as long as we understand how it works, and now we do thanks to both of you who participated the discussion! I thought I did it all wrong, it is kinda strange nevertheless.