> zypp-head:~ (0) $ zypper locales
> Reading installed packages...
> Code | Language | Requested
> -----+----------+----------

> zypp-head:~ (0) $ zypper addlocale en_GB
> Loading repository data...
> Reading installed packages...
> Added locale: en_GB
> Resolving package dependencies...
> 
> Nothing to do.

> zypp-head:~ (0) $ zypper locales
> Reading installed packages...
> Code | Language | Requested
> -----+----------+----------

Still no locale. Probably because the empty (no packages) commit was not
executed. 


> zypp-head:~ (0) $ zypper addlocale --no-packages en_GB
> Loading repository data...
> Reading installed packages...
> Added locale: en_GB

> zypp-head:~ (0) $ zypper locales
> Reading installed packages...
> Code  | Language                 | Requested
> ------+--------------------------+----------
> en    | English                  | Fallback 
> en_GB | English (United Kingdom) | Requested

Looks like --no-packages triggers an empty commit, which does update the
metadata files even if no packages are to be installed.

(Also check removelocales. Commit must be executed if the language set changed,
even if no packages are to be handled)