Can my portal show prices in a different currency if my customer is from another country?

Yes, in most cases your portal can show prices in a currency other than your own, but how far that goes depends on your suppliers and your payment setup.

The usual way it works is that your portal has one base currency, the one your suppliers bill you in, and a conversion rate is applied on top so the customer sees a familiar currency while they search. You can normally choose which currencies to offer, and whether the customer picks one themselves or the portal guesses from where they are browsing. Rates are refreshed from a rate source on a schedule, and many agencies add a small buffer to the rate so a movement between the search and the payment does not eat into their margin.

Where it gets less flexible is the actual charge. Some suppliers will only confirm and bill in their own currency, and your payment gateway may only be able to collect in the currencies your bank account supports. So a customer can often see the price in their own currency while the money is still taken in yours, and their card issuer then does its own conversion. The voucher or ticket may also still carry the supplier currency, because that is what the airline or the hotel issued.

Whether you can genuinely settle in a second currency comes down to your gateway, your bank and your plan, so check first which currencies your payment gateway and bank account can accept, then ask which of your connected suppliers can confirm in those currencies.