Is Chinese a single language?

Pro

 * From the writing system perspective, Chinese would be a single language. Thus, if we disregard pronunciation and only observe the language production as manifested in writing, the mutual unintelligibility of the dialects or varieties disappears or becomes greatly reduced. (Needs a double check by an expert or a good sourcing.)
 * In a human language, pronunciation precedes writing and appears more constitutive of it than writing.
 * On the other hand, for the purpose of creating an information system of languages, which necessarily depends on writing rather than pronunciation (especially when the writing does not correspond to pronunciation but rather has it origin in something like idea-script or concept-script), it may turn eminently practical to treat Chinese as a single language. This would explain why e.g. Google Translate has "Chinese (Traditional)" and "Chinese (Simplified)" but no "Mandarin", and similar treatment is in Bing translator.
 * Since, according to Britannica, certain variety of Mandarin is the basis for Modern Standard Chinese, it could be that these translation services actually work with Modern Standard Chinese or Chinese/Mandarin rather than Chinese as encompassing e.g. Cantonese; requires clarification. In any case, in the direction from e.g. English to Chinese, these translation services do not allow the user to indicate whether the target is Mandarin or Cantonese, and since there are some--even if small--vocabulary differences between Mandarin and Cantonese, the use of Modern Standard Chinese by these services seems plausible enough.

Con

 * Since the putative dialects of Chinese are not mutually intelligible, they are not part of a single language. (For instance, Cantonese and Mandarin are mutually unintelligible. )
 * Chinese is treated as multiple languages by Britannica and Asia Society. That is not conclusive but is suggestive.