My Problem is, that it scans source files on disk an try to find it out of it. This is a huge text analysis because themes/plugins need not to be activated to deal with this. So I need a ways to be sure about standards of utilization of files to be generated.
Even if this could be hooked the standards is:
function load_theme_textdomain( $domain, $path = false ) {
$locale = apply_filters( 'theme_locale', get_locale(), $domain );
$path = ( empty( $path ) ) ? get_template_directory() : $path;
$mofile = "$path/$locale.mo";
return load_textdomain($domain, $mofile);
}
This implies, that any language file for Themes (in opposite to Plugins) only consists of "$locale.mo", in german case "de_DE.mo"
This is what I call standard.
I know your problem by updating parent theme and loosing the user modified translations but your localization would also work as done, if you would use the standards like "de_DE.mo" instead of "hybrid-de_DE.mo" (which is plugin naming).
Nevertheless I'm also working on a proper way how WordPress can fulfill your need out of the box. If it's working stable, I will put the patch.diff to the trac.