Comment # 1 on bug 966066 from Michael Andres

Of course it is possible to ignore recommends; we have zypper cli options for
this, you can disable solving recommends in YAST and turn them off per default
in /etc/zypp/zypp.conf.

And it's also possible that any lang package was uninstallable at the time gimp
was installed or it has been deleted afterwards.

Please try:

== zypper wp gimp-lang
to check there's actually no package providing it installed

== zypper in --recommends -f gimp
to re-install gimp with recommends turned on for sure

== zypper in gimp-lang
to check whether gimp-lang is actually installable in case the gimp re-install
did not select it.