Since you are not in the business of currency trading, you do not get to deduct for "losses'. So in your case -- you have a property in Russia which  was originally bought for XXX Rubles --- this is your basis in the property in US$ on the day of the transaction.  If and when you sell the property, the gain in US$ would be ---- > Sales price  LESS sales expenses LESS your adjusted basis in the property. The adjusted basis is the  original basis  plus cost of any improvements  LESS  accumulated allowable depreciation --- all the  Rubles need to be converted to US$ of the day ( i.e. time of the transaction / action).  Your mortgage payments  are  recognized  as expenses/ deduction   either on schedule-E ( if you rent out the property ) or as second / vacation home ( if you  use the property as such).  There are many other variables / situations to consider -- therefore the answer is rather general in nature.

hope this helps