[charlesdm]

Depends on the tax and accounting laws of your country, but generally the taxable event happens when you invoice.

So I'm doing accounting in EUR and invoice 10,000 USD. For accounting purposes my 10,000 USD gets converted to EUR on the invoice date, at the ECB USDEUR exchange rate.

Then you hold that 10,000 USD for 2 months in your USD account, and the USDEUR exchange rate has dropped or increased 10% in that period. When you then exchange the USD into EUR, you'll generally pay tax on the exchange difference (= capital gain)

My Belgian bank accounts are all multi currency. I can hold, receive and send USD/EUR (and others if I wanted to).

[EastSmith]

Thanks, the exchange difference indeed looks like capital gain.