It was my impression Huntsman spoke conversational Mandarin, but he wasn't fluent. Whenever he gives complicated speeches, he says a few sentences, and then transitions back to English.
Huntsman did is mission in Taiwan, so he probably was fluent at some point, well, with the standard southern accent. FYI, diplomats and leaders will typically use their official language regardless, even if they are fluent in their host country’s language. For example, the prime minister of Singapore is definitely fluent in mandarin, but always will use English for official communication.
