Mandarin

Area in China where Mandarin is commonly spoken (light brown)

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

Appearances in The Big Bang Theory

• Howard claims to speak Mandarin. In The "Pilot" He tells 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 "The 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 teach Sheldon Mandarin, causing Sheldon to speak several ridiculous "Mandarin" sentences in the episode, and finally 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 "The Dumpling Paradox", the words he mumbles to himself when he leaves the three guys sounds like a dialect of Chinese (possibly Cantonese). Also, his words at the end of "The Tangerine Factor" "Xing gan jing bi ti hou, kuai zou kuai zou!" (literally "Blow your own nose and go away quickly") is a little stiff and not so natural to be Mandarin.
• In "The Hawking Excitation" (S5E21), Howard rejects Sheldon's request to see Stephen Hawking in several lanugages, including Chinese "不" (meaning "no", pronounced as "bù").
• Allegedly Penny has a Mandarin character tattooed on her bottom (it's also possible that it could be Cantonese). Sheldon, who has seen her naked, dispassionately interpreted it as meaning "soup".