Request for i18n review of PubSub

Hi Addison, Richard, and everyone,

PubSub (previously known as PubSubHubbub, and possibly facing a new name
change soon) recently entered FPWD. It's been incubated for several years,
and so we think the current state of the draft will be fairly stable.

https://www.w3.org/TR/pubsub

We would very much appreciate an i18n review at your convenience.

Protocol summary:

The subscriber discovers the target's *hub*, and sends a form-encoded POST
request containing values for *hub.mode* ("subscribe"), *hub.topic* and
*hub.callback*. The hub verifies this request. When the target posts new
content, the target's server sends a form-encoded POST to their hub with
values for *hub.mode* ("publish") and *hub.url* and the hub checks the URL
for new content and subsequently delivers updates to the subscriber's
callback URL.

You'll notice it's based around a finite set of English language strings
for both keys and values which are passed around. Given this is entirely an
internal data passing mechanism, I don't know if it raises i81n problems.
Maybe it does. The editor (Julien) went through the self-review checklist
and noted:
 * The checklist seems to be strongly oriented toward HTML/formats when we
are mostly providing a “transport" protocol.
 * It is not clear whether it’s ok to have English word in our syntax. It
would not make sense to have parameters “translated” here.
 * Error messages are returned in English - they're intended only for
developers to see, do they need a localization mechanism?

Thank you,

Amy