<ww:textfield label="'i18n.label'" name="'label1'" value="''">
This will get the localized text message for the key "i18n.label" and put it in the label.
<ww:textfield label="getText('i18n.label')" name="'label1'" value="''">
Alternatively, you could modify controlheader.vm and copy it to /template/xhtml. There you could make it so that it automatically does a call to $stack.findValue("getText($parameters.label)"), making the first example actually work for i18n.