Borrowing in an additional currency to that which you receive rent in is not advisable for investment.
Definitely agree with David about the risks. There is a mortgage broker where I live who constantly harps on about Swiss Franc mortgages and multi-currency advantages, advertising them in the local press so lo and behold every body asks me if they can have one as well...
Unfortunately he does not maker the risks apparent.
The first question I ask a client is "Why do you want that?"
Generally they don't really know or tell me because they read about them somewhere and it said the interest rate was much lower.
I think people incorrectly presume that because the Swiss currency is "stronger" or "more stable" then there is little risk. What they tend to forget is that it doesn't matter how stable the Swiss Currency is if the currency you earn in is NOT Swiss francs.
If Swiss Francs appreciate against Sterling for example - your payments go UP!
A good example of the risks is all those who have purchased with Spanish mortgages - obviously denominated in Euros. As the Euro hasd strengthened against the pound - their mortgage payments in Sterling have increased.
This combined with an increase in the Euribor has a had a hefty impact on mortgage payments.
Most banks wont actually do multi-currency for a general mortgage client as they are too risky but if you are a sophisticated investor who understands the risks or you have a valid requirement for a different currency then they can be arranged through banks and/or private institutions.
I am doing one right now for a client who
does have a specific requirement to switch currencies and fully understands the ins and outs of it all.