Some UI components do not fallback to the default locale resources when no resources are found for the current user locale.

If you add a locale, for which cms resources are not translated yet, and log on by the new locale in the login page, then most wicket components show labels properly from the default locale resources, but some UI components such as accordion in the cms dashboard doesn't show the default locale resource strings instead.
Also, in the login page, it doesn't show proper locale name for something new. e.g. "cy" for Welsh (Britain) language.