Global <em:creator> isn't used for new installed extension, if browser...
I know it, probably i was not so clear previously.
Creator's name should be appear of course in extension's "About",
even when the extension has been localized.
In my first post here i meant that, if a name is not localizable, e.g.
because it's a nickname in English, then it's not necessary the "<em:creator>"
item to be included among the items to be localized, on WTS.
You can just put it in every "<em:localized>" section in your install.rdf,
letting only the localizable items to be managed by the translators, putting
them on WTS.
For more documented details, you may be interested to take a look here
and then consider which of them can be eligible to be localized and
put them on WTS.
In my opinion, the most common localizable entries in "<em:localized>" section,
are the extension's name ("<em:name>", if applicable, depending of the locale),
"<em:description>", "<em:translator>" and maybe "<em:contributor>".