Manual:$wgNamespaceAliases

Details
These are alternate names for the primary localised namespace names, which are defined by $wgExtraNamespaces and the language file. If a page is requested with such a prefix, the request will be redirected to the primary name.

Set this to a map from namespace names to IDs. Example:

To add a single alias:

Do not use space
Take care: If you must define a namespace which contains a space character, use an underline instead. For example 'My Namespace' is an invalid name and it is likely to create many problems. Use 'My_Namespace' instead.