How can you even expect him to communicate properly with a native speaker without a translator?
He's not some bum from the street. He's the president of a 42 million strong country, and the biggest state in Europe (outside Russia).
He could bring with himself 100 interpreters if he wanted to... If Ukraine has so little money - there's probably 20,000 Ukrainians living in and around Washington D.C. that would happily volunteer to translate for their president.
No, this was Zelensky's decision. He decided that its better for him to carry on the conversation with Trump and Vance in English.
From his eyes, and his facial expression it is absolutely clear that he did not understand what Vance meant when he said, "there is no need to relitigate this matter in front of the media".
Then, what got Trump really going, is when Zelensky started replying to Vance: "... you think if you speak loudly". As a Russian speaker, I know what Zelensky wanted to say. He wanted to say, "You think if you speak loudly from every platform that Putin is a nice guy with whom we can make a deal, that he will reciprocate?". Unfortunately, in colloquial English if you begin telling someone "you think if you speak loudly", people assume you are talking about their tone of voice. Zelensky had no way of knowing this, neither did Trump. Trump interjects, and defends his VP, and says "he was not speaking too loud".
A complete clusterf*ck. Nobody understands each other, and are talking past each other.
These are just two examples. Its also clear Zelensky fumbled the response on wearing a suit, and several other things.
He did not have to speak English.
The problem with this guy is he doesn't speak any language well. His Russian is street Russian, full of ugly turns of phrase. His Ukrainian is subpar, since he started learning it four years ago. His English is sh*t.
Zelensky doesn't speak any language well.
