Mandarin

Mandarin is the standardized Chinese language in most part of China.

• Howard claims to speak Mandarin. In The Pilot Howard tells to Penny to have a "good shower" in French and Mandarin. But the "Mandarin" he speaks (Xi ge tong kuai zao!) is quite twisted in pronunciation.

• According to a comment from Mr. Chen in The Dumpling Paradox, Howard's Mandarin is actually very poor:

Chen: Where is your annoying little friend who thinks he speaks Mandarin?

• The "Mandarin" that the two "Chinese" speak at the end of Cooper-Hofstadter Polarization is fair in pronunciation, but is far from authentic. It is very clear that they (or say, the two actors) are not native Chinese speakers.

• In The Tangerine Factor Howard tries to teaches Sheldon Mandarin, but fails as evident from the final dialogue between Sheldon and Chen. Interestingly, Sheldon does utter a quite authentic Mandarin sentence "Aiya, xia si wo le!" (literally "Alas, I'm frightened！"） to Penny in this episode.

• As to Mr Chen, he can speak Mandarin, but seems not to be a native speaker. In Dumpling Paradox, the words he mumbles to himself when he leaves the three guys sounds like a dialect of Chinese. Also, his words at the end of Tangerine Factor "Xing gan jing bi ti hou, kuai zou kuai zou!" (literaly "Blow your own nose and go away quickly") is a little stiff and not so natural to be Mandarin.