Jimmy (Jimbo) Wales wrote:
Within a fairly wide range, though, such differences can be avoided in an encyclopedia. It depends on how extreme the differences might be, of course, but mutual intelligibility is the standard that I would use.
Mutual intelligibility is sort of a gray area though, and in this particular case seems to be even more problematized by the political issues---some people have a vested interest in making Chinese appear more like one language than it really is, and other people have a vested interest in making Chinese appear less like one language than it really is.
To take just one data point, many of the Chinese I know who emigrated to the US 50+ years ago find it very hard to understand contemporary Chinese written in mainland China, but generally have little trouble understanding contemporary Chinese written on Taiwan. One of them even compares the two languages by saying Traditional Chinese with Taiwanese vocabulary is analogous to Latin, and Simplified with Beijing vocabulary is analogous to Italian --- they share a common origin and many similarities, and educated people can understand both, but they're different languages. Obviously, this is a minority viewpoint (although many linguists do dispute the claim that there is a single language called "Chinese", and assume non-linguists claim that there is exclusively for political reasons).
-Mark