[[MediaWiki:Interlanguage-link-commons/en]], [[MediaWiki:Interlanguage-link-wikipedia/en]] etc
For some unknown reason, some of these (Special:PrefixIndex/MediaWiki:Interlanguage-link-) appear to have been marked "optional". This is incorrect. You can see on e.g. Russian Wikivoyage that the translation for "Wikipedia" in the sidebar is missing, because translators have ignored it.
Nikerabbit: Ping?
No point in pinging. Marking optional is correct, because some/most languages don't need to translate the names.
As I see it, a significant proportion languages do indeed have a local name for Wikipedia that differs from the English name. See [1]. Translators don't appear to translate optional messages, which makes me wonder what the point of them is?
The point is not harassing translators continuously by telling them that a message is untranslated (both in Special:Translate and in statistics) when the message doesn't require translation. Your link shows 160 titles different from "Wikipedia", but for instance that includes 12 occurences of "Википедия" which only needs to be translated once in Russian for all the others to pick it up.