If you have to deal with foreign exchange rates with every mortgage payment, it certainly makes more sense to get the mortgage in the country the property is located in. Then you deal with 2 exchange rates instead of 3.
In the USA, I would not recommend an adjustible rate mortage. Fixed rates are good right now, and it is very unlikely that an adjustable rate will adjust in any direction but up.
In my opinion, interest only loans are only sensible when you are going to hold the property for a very short period. 6 months or, at the very longest, one year.
Some of us in the USA think we have an inflationary period coming. If that happens the fixed rate loan gets paid back with cheaper dollars. Certainly good for investors inside the country, although I am a little uncertain how that works with foreign exchage. I would think you would be able to buy more dollars with your pound or euro, making the loan payments cheaper for foreign investors, too.