Translation:The interpreter probably understands what he is saying.
I find this ambiguous. Does it mean:
1.) Does the interpreter understand what he (himself) is saying?, or
2.) Does the interpreter understand what he (someone else) is saying?
In English we might say, "Do you think he understands what he's saying?" meaning, does the speaker understand the gravity of what he (himself) is saying? Or, is the speaker babbling on without actual knowledge?"
You cannot use sin because it means his (or hers or its depending on who it points back to). So it would be like saying the interpreter doesn't understand what his is saying. Since we can't use that here, the sentence is just as ambiguous in Swedish as in English.
If we rewrite the sentence so that we could use his in English, we would get to choose between sin and hans in Swedish and then we could make it unambiguous. Like, The interpreter doesn't understand his statement – ambiguous vs. Tolken förstår inte hans/sin utsaga or hans/sitt uttalande – unambiguous.