While I'm at it, can you please tell me how you handle the currency exchange in the Balkan countries that don't use the euro? I will probably get a Revolut credit card, but I wonder whether any countries have no-commission booths, Thai-style, where I can change euros.
Thank you. My question was to know how to go about changing into these currencies from euros in cash.
Much depends on your personal financial situation. You mentioned the Revolut, that is a prepaid card, not sure of the details of that card, but typically that is not a cheap option, you pay to get the card, to load money on, to use the card, then if you have money on the card over time, they charge a fee to keep it active; so understand your costs.
If you have an ATM or banking card, that is really all you need. Again, depends on your bank and the fees they charge, but getting local currency from an ATM can be the cheapest route (watch for use fees and DCC)
I would also have a traditional credit card and use that as much as possible.
Revolut is technically a pre-paid card, but operates more like a bank account. Transfers between currency wallets (or direct payment out) are fairly close to the interbank rate if you don't do it on a weekend, and there aren't any on-going charges.
Last time I was in Croatia - August 2018 - I saw a few currency exchange booths around. Zagreb airport had one. They still exist but not as many. I doubt you will find any with no-commissions.
Just get decent credit and debit cards that offer current exchange rates without foreign exchange fees (they are out there), and then use them to purchase or take cash out of ATMs. Its very simple.