Formatting plural on Shapado and Open Street Map

> Shouldn't the messages have '0' instead of 'zero'?

No.

> You should always use all n forms if your language has n forms. No more, no less.

If an English message uses 'zero' do all languages have to use 'zero', regardless of whether 'zero' is defined for their language or not?

I really don't know. I have no knowledge of the inner workings of rails i18n.

All languages support a key of 'zero' which is handled outside of the language specific pluralizers as seen here:

So if the value is 0 and a key of "zero" exists then it is used, otherwise the language specific pluralizer is called.

And so, if an English message uses 'zero', do all the translations have to use 'zero', even if they don't actually need it?

Not at all - if there is no "zero" key for a given language then that languages normal pluralization rules are used to select a key.

Thanks for setting me straight.