[Y_Y]

I interpret RFC 3339 not to apply exclusively to machine-to-machine communication. Specifically section 5.3 includes the following:

> a balance must be struck between human readability and interoperability.

and

> Internet clients SHOULD be prepared to transform dates into a display format suitable for the locality.

(where SHOULD is used in the RFC 2119 sense equivalent to RECOMMENDED).

[happytoexplain]

Human readability does not mean end user readability. It's good if humans can read it so that programmers/admins can read it, and also end users if they happen to be exposed to it. But for display to end users, it should always be formatted in a localized, naturally readable manner with no concern for machine parsing (which is what the second quote is referring to).