I'll give an example here of how Chinese characters reflect speech more than they reflect meaning-as-such. Many more examples are possible. How you might write the conversation
"Does he know how to speak Mandarin?
"No, he doesn't."
他會說普通話嗎？
他不會。
in Modern Standard Chinese characters contrasts with how you would write
"Does he know how to speak Cantonese?
"No, he doesn't."
佢識唔識講廣東話？
佢唔識。
in the Chinese characters used to write Cantonese. As will readily appear even to readers who don't know Chinese characters, many more words than "Mandarin" and "Cantonese" differ between those sentences in Chinese characters.
[1] http://www.amazon.com/Chinese-Language-Fantasy-John-DeFranci...
[2] http://www.amazon.com/Visible-Speech-Asian-Interactions-Comp...
[3] http://www.amazon.com/Ideogram-Chinese-Characters-Disembodie...
[1] http://news.xinhuanet.com/english/2007-03/07/content_5812838...
In other words, hundreds of millions of persons in China cannot have a telephone conversation with one another, or ask for directions and get a comprehensible answer if they travel to each other's home regions, and so on. National common language promotion in China still has a very long way to go (although of course it is farther along in the younger generation than in the older, and farther along in urban areas than in rural areas). For this issue of national policy, the relevant issue is whether or not people can understand one another when they have a conversation. Many, many, many groupings of citizens of the P.R.C. would include people none of whom have a common language mutually understood by any other person in the group.
By contrast, Taiwan has been much, much, much more successful, much earlier in history, in making Modern Standard Chinese (Mandarin) a common language in a region where historically "Taiwanese" (the Taiwan dialect of Southern Min Chinese) was the majority language and Hakka was a significant regional minority language. After 1949, when the defeated Nationalist forces retreated to Taiwan, perhaps 10 percent (mostly soldiers) was added to Taiwan's population, but not all of those persons were speakers of (mutually understandable) Mandarin either, yet Mandarin was thereafter treated as the sole national language in Taiwan. My wife grew up speaking Taiwanese to her parents (who spoke Japanese to each other, because of their prewar education in occupied Taiwan, then a colony of the Japanese empire), and Mandarin to her siblings and classmates. I met her in 1982. She spoke perfectly adequate (Taiwanese-accented) Mandarin as young adult, and she often impressed visitors from the P.R.C. to the United States in the mid-1980s when we were both students with the quality of her Mandarin. My nieces are now generally more proficient in Mandarin than in Taiwanese, although both languages are still used among our relatives in Taiwan. (Mandarin and Taiwanese are cognate Sinitic languages, but no more similar than English and German are, and certainly NOT mutually comprehensible.) Taiwan achieved much more rapid spread of Mandarin by having a stronger economy in the 1950s, 1960s, 1970s, and 1980s, and thus much more use of personal telephone calls and radios and televisions and much more internal travel. China still has a lot of catching up to do.
The book The Chinese Language: Fact and Fantasy by John DeFrancis
http://www.amazon.com/Chinese-Language-Fantasy-John-DeFranci...
does a lot to disentangle the issues of speech versus writing, and dialect versus language, that are discussed in several of the interesting comments that preceded my comment here.
Here's an example of how you might write the conversation
"Does he know how to speak Mandarin?
"No, he doesn't."
他會說普通話嗎？
他不會。
in Modern Standard Chinese characters. Contrast that with how you would write
"Does he know how to speak Cantonese?
"No, he doesn't."
佢識唔識講廣東話？
佢唔識。
in the Chinese characters used to write Cantonese. As will readily appear even to readers who don't know Chinese characters, many more words than "Mandarin" and "Cantonese" differ between those sentences in Chinese characters. Even the traditional Chinese character writing system doesn't bring about mutual understanding among people from all parts of China.
How you might write the conversation
"Does he know how to speak Mandarin?
"No, he doesn't."
他會說普通話嗎？
他不會。
in Modern Standard Chinese characters contrasts with how you would write
"Does he know how to speak Cantonese?
"No, he doesn't."
佢識唔識講廣東話？
佢唔識。
in the Chinese characters used to write Cantonese. As will readily appear even to readers who don't know Chinese characters, many more words than "Mandarin" and "Cantonese" differ between those sentences in Chinese characters.
Chinese characters still represent SPEECH (not ideas or abstract concepts) and do so in a way that is specific to the particular Chinese (Sinitic) language that one speaks. The long story about this can be found in the books The Chinese Language: Fact and Fantasy[1] or Visible Speech: The Diverse Oneness of Writing Systems[2] by the late John DeFrancis or the book Ideogram: Chinese Characters and the Myth of Disembodied Meaning[3] by J. Marshall Unger. The book Reading in the Brain: The Science and Evolution of a Human Invention[4] by Stanislas Dehaene is a very good book about reading in general, and has a good cross-cultural perspective.
Many other examples of words, phrases, and whole sentences that are essentially unreadable to persons who have learned only Modern Standard Chinese can be found in texts produced in Chinese characters by speakers of other Sinitic languages ("Chinese dialects"). Similar considerations apply to Japanese, which is not even a language cognate with Chinese, and also links Chinese characters to particular speech morphemes (whether etymologically Japanese or Sino-Japanese) rather than with abstract concepts.
[1] http://www.amazon.com/Chinese-Language-Fantasy-John-DeFranci...
[2] http://www.amazon.com/Visible-Speech-Asian-Interactions-Comp...
[3] http://www.amazon.com/Ideogram-Chinese-Characters-Disembodie...
[4] http://readinginthebrain.pagesperso-orange.fr/intro.htm