I don't know anything about Montenegro but this might kick start the tread for you
Well I know you will have to pay tax on the rental income(less usual deductions as per Irish property ie mortgage interest, 12.5% F+F, maintenance ) in Ireland as if the property was in Ireland. When you sell the property you will have to pay Irish Capital Gains tax (less usual deductions) as if the property was in Ireland.
You will of course have to pay all the relevent taxes in the Foreign country.
It's now a case of finding out how much of the tax paid in the foreign country can used to reduce your tax liability in Ireland. Previous contributors to AAM have suggested that if no double tax agreement exists then you have to pay full tax in both countries. I don't think this is correct. I'm not 100% sure but the extract below from revenue.ie form IT70 seems to suggest that you can avail of deductions against your foreign Rental Income Tax for tax paid abroad. There is no mention of double tax agreements needing to be in place.
I do know that you cannot offset Irish rental losses against foreign rental profits and vice vearsa as they are different cases of income.
Revenue.ie Form IT70
"In general, income from foreign property is computed on the full amount of the income arising, irrespective of whether the income has or will be received in the State. In the case of foreign rental income this income is charged under Case III of Schedule D and the same deductions and allowances are available as if the income had been received in the State. Deductions are also normally available in respect of such income for sums in respect of foreign tax paid. This income should be included in an individual’s tax return on the Foreign Income panel."