No, Donorbox does not have any fee associated when withdrawing currencies that are different than your own. Additionally, neither does Stripe or PayPal.
Rather, "fees" associated with withdrawals of currencies via Stripe or PayPal will be a result of currency conversion. For example, if your organization is from the US (USD) and you were to receive a donation from Canada (CAD), Stripe or PayPal would automatically convert that amount to USD when it's transferred into your account.
As currency prices fluctuate consistently, it's not possible to know in advance what exchange rate you will pay. For this reason, when Stripe or PayPal performs a currency conversion, by default the conversion rate will be 2% higher than the most optimal rate. Furthermore, Stripe and PayPal merchant accounts charge 2.9% + $0.30 for credit card processing for all donations. These fees are deducted immediately. Stripe fees may be discounted down to 2.2% + $.30 (Stripe) or 1.99% + $.49 (PayPal) for registered nonprofits.
Click here for more details on Stripe's currency conversion process.