Comment # 1 on bug 980583 from Dominique Leuenberger

The implementation idea would be:

- give find-lang a new pamatered (--metainfo [<desktopID>])

if this parameter would be passed, a new, minimal metainfo.xml would be written
ot %{buildroot}%{_Datadir}/appdata/%{name}-lang.metainfo.xml, containing
information like:

> <?xml version="1.0" encoding="UTF-8"?>
> <!-- Copyright 2016 openSUSE - file is auto-generated -->
> <component type="addon">
> <id>%{name}-lang</id>
> <extends><desktopID></extends>
> <name>Translations for %{name}</name>
> <summary>Allow to run %{name} in other lanuages</summary>
> <metadata_license>CC0-1.0</metadata_license>
> <updatecontact>bugzilla.opensuse.org</updatecontact>
> </component>

and of course add the file to the files-list (as captured by %{name}.lang)

if <desktopID> is not specified, we would 'search' for a .desktop file in the
installed files list and, IFF one (and only one) desktop file is found, use
this as the guessed value. If more than one file is found and --metainfo
requested, this would be treated as failure (no valid guess possible)

@mls: what do you think of this approach? 
(if you agree, I will work on the implementation of this for openSUSE)