It is not a problem at all, if you trade in foreign currencies.

You can also do that within one account, since it doesn't make any difference if you separate the data, 

unless you need to pay taxes in a foreign currency, or rather in another country.


What you need to keep in mind, is that you need to enter the trades for your foreign currencies.

Most of the time exchanges do not list these transactions as trades.


For example:

If you send Euros to BX, it could happen that BX converts them for you and Thai Bahts arrive in your account.

You need to enter a "Trade" of "Buy Baht and Sell Euro".

If you don't do that, your purchase pools are not being filled and this leads to warnings and mistakes in the gain and tax calculation, 

when selling them later.