Unless this message is empty, this is used as link target in the last entry, also known as the footer, of the outer Babel-box, provided that the installation chooses to have a footer. The corresponding link anchor is the message babel-footer ("Users by language").
For installations having a 'Babel users per language' category tree, its root should be entered here. When translating, you can copy the category name from existing Babel systems in your language, but you can as well use a more generic name and leave it to individual installations, how to deal with it.
There is no need to alter the name space name