A second source claims CNN mistranslated Iranian President's comments

Tom in London wrote:

It seems to have become a common trick to claim that Iranian leaders are not being correctly translated by their interpreters. Never the leaders of any other country. I find this quite interesting.

Teresa Borges wrote:

Isn't Iranian (also referred to as Farsi) Iran's official language?

Samuel Murray wrote:

Well, there is the power issue. Even if the interviewee is "pretty good" at English, he'd still be at a disadvantage (from a power point of view) when the interviewer is a native speaker of English. Any person is usually most powerful in his native language. If a person speaks a foreign language, he is less at ease.

The fact that a person is "fluent" in English doesn't mean he can speak with ease on any topic in English. The usual language of politics in Iran is not English, so you can't expect Mr Rouhani to be as fluent on political matters in English as he is in the language of his country.

If the South African president were interviewed, you can bet that he'll speak English and not his native language, because English is the language of politics in South Africa. But English is not the language of politics or indeed the language of anything in Iran.

I recall watching an interview with a Dutch politician who went to the US. He thought that he could speak English fluently (and he was pretty fluent), but he was unable to think on his feet quite as smartly as he could in Dutch, and if it wasn't for his celebrity status, people would have though of him as a complete dunce... because he chose to speak a foreign language in which he was "fluent".