How can I exclude links to untranslated pages from Google search results?
When using i18n xml sitemap, and when you have a menu set to be included in a sitemap (using xmlsitemap menu), even if that menu is set to display only for one language (localized to Japanese or English in my case using i18n_menu), it will still get added to the sitemap for both languages.

So, in this case, one solution is to avoid using xmlsitemap_menu and instead use xmlsitemap_node and add the node links individually.

Painful but it works.