This is a clip of Mark Zuckerberg's more than 20-minute speech at Tsinghua University in Beijing. According to the Facebook founder and CEO, this was his first time giving a speech in Chinese. (Tsinghua University)

Last October, Facebook chief executive Mark Zuckerberg won widespread praise for holding a question-and-answer session at Beijing's Tsinghua University almost entirely in Mandarin. Although many experts agreed that his language skills were far from perfect, the audience was clearly delighted when the American billionaire first began speaking in Mandarin, which he has been learning since 2010.

Almost exactly a year later, Zuckerberg decided to show off how far his language skills have progressed by giving a 20-minute speech entirely in Mandarin. Speaking to Tsinghua students again, he talked  about Facebook's history and his sense of its bigger purpose.

"This was also my first real speech in any language sharing how I started thinking about Facebook's mission, what has kept me going through challenging times and what our mission means now looking ahead for our community of 1.5 billion people," Zuckerberg said in a message posted to Facebook.

Facebook has been blocked in China since 2009, though some in the country access it via virtual private networks. Many observers believe that Zuckerberg's efforts to learn Mandarin are part of a broader plan to gain access to the country, which has a population of more than 1.3 billion. The Facebook CEO used his language skills to speak directly with Xi Jinping during the Chinese president's recent visit to the United States.

A link to Zuckerberg's speech was shared on Sina Weibo, a homegrown social network popular in China, and users' reactions were mixed. Many expressed admiration for his attempts to learn Mandarin, but not all thought his skills were quite so impressive. "If it were not for the English subtitles, I really couldn't understand him," one user wrote. "This Mandarin is really difficult to hear," another added.

Others, however, were more amused to see so much talk about the head of a Web site they couldn't even access. "Who is this person?" one user mocked. "Is there a Facebook Web site in this world?"

Another poster referred ironically to the error page that appears when Chinese users try to load Facebook: "404 is coming to China."

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Xu Yangjingjing contributed to this post.