B757 Captain reported a communication breakdown between Captain and Tug driver during pushback due to the Tug Driver's poor English language fluency.

Narrative

Parking [Brake] was not set while starting engines and not attached to tow bar.Tug driver's English was broken and it was obviously not his first language. The exchange between myself and driver was non standard and heavily accented. We could tell the push was almost complete because our speed was slowing as we approached spot XX. Driver said something about spot XX and that we were cleared to start. Nothing about setting brakes. It made sense to me at that point because we weren't completely stopped. FO began to spin #1. Airplane did stop and I hadn't heard anything about brakes. But when I heard the tow bar drop from nose I quickly asked if he wanted brakes set. There was not an immediate response and I wanted to have the airplane restrained before fuel was added; so I set the brakes before I actually heard back from driver. My exchange with him was now in plain English; 'Do you want the brakes set? 'There were several exchanges of me asking if he wanted brakes set and him responding with 'The brakes are set?' Note that his responses were a question. When asked when he told me to set brakes it appeared that he understood that he said we were approaching spot XX and cleared to start that this meant the push was complete and I was supposed to set the brakes. When I mentioned I don't set the brakes until he uses those exact words he seemed perplexed. Perplexed in a way that seemed to me he didn't understand what I was saying. His grasp of understanding English was clearly a problem. My feeling was that I would not have been able to any kind of conversation with this person outside of very specific wording. His assumption that I was going to set the brakes when we stopped is way beyond the SOP.