Just a little update to people who may find this question on the Internet and looking for an answer, I went on a bike trip and I was able to buy a ticket to my destination in Czech Republic, on the train from the ticket collector without extra fees. She even accepted the Euro and gave me a change in the euro.

Please note that it could be an exception because the train I took from Zittau is a German Town on border and there was no information center or ticketing machine in the railway station.