In the acs-lang/admin/edit-localized-message form, the message key value is required. However, the Tcl and SQL APIs don't require this. It is possible to create and set a blank message key value via the API.

I suggest making the admin form and API consistent by making the message key value field optional.

A blank message key may be useful in some cases.
For example, in number formatting keys like acs-lang.localization-thousands_sep, the value may be comma, period, or blank depending on the locale or preference.

Can anyone think of a problem allowing blank message keys to be entered from acs-lang/admin?