when calling lang::util::convert_to_i18n, do not always register a en_US translation, which will be otherwise always overridden. Instead, let lang::message::register make sure that a en_US message exists and create it only when needed as a fallback. Before, lang::message::register would return an error when e.g. a new message keys was registered for de_DE and no en_US was there. Now the en_US will be just created on the fly.
Provide an optional object_id which can be used to register message keys that will be bound to the lifecycle of an acs-object. When the object is deleted, so will the message key. This is useful for groups that automatically define a message key for their pretty name. Tcl api was already aware of this and would cleanup such message keys, but other idioms e.g. stored procedures used to delete groups would leave leftovers behind. These can become relatively numerous on group-intensive systems such as LEARN.
Other future usages for this new feature might be the automatic localization of xowiki FormPage properties.