Wrong in this context.
1. People who speak other dialects like Cantonese overwhelmingly use the same written language, so there's no barrier in written communication;
2. AFAIK Mandarin is the mandatory teaching language in Mainland Chinese schools, so even if you want to be pedantic I'd say 1 in 5 has native or bilingual proficiency in Mandarin.
> starting a manderin only software project would mean choosing between only Chinese developers and Chinese devs and the rest of the planet as well.
First, there's no such thing as a "mandarin-only software project", you use Chinese the written language as explained above.
Secondly, it's still a reasonable choice if the author finds the alternative mentally draining, or the primary audience does. No point in global-proofing your project if the primary audience need to spend extra time and energy to communicate worse. I don't necessarily advocate for it, but I don't pretend that every project on earth has the obligation to make it convenient for me to contribute.
>You can already see this happening with some open source libraries coming from China, where the documentation and all discussion being in ZH already completely blocks foreign contribution.
You
>Given that one in five person on the planet speaks Chinese as their first language, lack of “foreign” contribution will probably work out okay for them.
The point is you are using number of native speakers as a proxy for the population of developers being sufficient to support development.
First thing is the single most popular l1 language in China manderin is more like 1 in 8 humans, next the distribution of talent is nothing like distribution of speakers. It looks a lot more like the distribution of wealth because access to computers during formative years or indeed at all is of substantial importance.
There are of course still many Chinese developers of substance. But because highly educated developers in China are both a smaller portion of the population and likely to speak English starting a manderin only software project would mean choosing between only Chinese developers and Chinese devs and the rest of the planet as well.