If original, or if rebarreled at some point by period military, it will be service 7.92x57 Infantry rimless. That was the standard Polish and German (and for that matter Czech and Iranian and so on!!) service round when it was made.
Best origin guess is, an arsenal somewhere in Europe converted it to a "sort of" K98k. Might've been the Germans, could've been the Czechs who exported a lot of "sanitized" rifles to the middle and near east for currency. Could've been the Turks or even some exporter.
If the barrel is in solid condition, it would not be a sin to "restore" it to some sort of facsimile of its Polish configuration, or as a German-style "Karabiner". That is, if the barrel hasn't been trimmed.