Maybe it is time to start reading topics in the GYM sitemap forum : gym-sitemaps-rss/
The fact that you see ACP_GYM_GOOGLE_MAIN in acp implies that you did not fully install the mod, at least for the language code changes.
Styling is only supported for prosilver so far, subsilver2 template will be added in next version. For xml outputs (rss and sitemaps), the styling is far from mandatory, you can deactivate it. Have you tried to load you forum css with sitemaps and feeds ?