I already paid tax abroad. Am I taxed twice?

Tax paid abroad can be credited against the Turkish tax attributable to that same income, so the same profit is not fully taxed twice. The credit has two limits. It cannot exceed the portion of your Turkish income tax that corresponds to the foreign income, so anything paid above the Turkish rate is simply lost. And it has to be evidenced by a document from the foreign tax authority, certified by the Turkish consulate in that country. In practice the credit is more often lost to the missing certificate than to the arithmetic.