Chinese languages or language?

I am a bit confused concerning the status of different varieties of
Chinese languages. More to the point, are Mandarin and Cantonese one
language, or two separate languages?

My understanding is that the written language is the same in both cases,
the difference being that ideograms are pronounced differently in each
variety. Is this right, or is there more to it?

If it is just a pronunciation difference, then one could trivially come
up with an unlimited number of varieties, just by assigning new, possibly
fanciful, pronunciations to existing Chinese ideograms. On this basis, my
inclination is to think that there is a single Chinese language, but I am
sure to be missing something here.


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