Since the introduction of s775 the general answer is, yes foreign exchange gains are taxable, and conversely foreign exchange losses are deductible. There are a range of exemptions and elections that can minimise or remove some gains or losses. The rules are relevant to all taxpayers and often have consequences for expats with foreign currency bank accounts or loans.

Converting currency, removing funds from bank accounts or repaying loans (in full or in part) triggers these provisions. Therefore check before you act! For more information, go here.