If you set your user language in the multilingual Wikisource to a non-English (and preferrably a non-Latin-script) language, like Arabic, some terms in the sidebar are not translated.
These messages should be added to WikimediaMessages, so that they can be localized properly.
- Step 1: Add the messages to the WikimediaMessages repo (patch)
- Step 2: Once the patch has been deployed (sourceswiki is Group1), edit MediaWiki:Sidebar to use the new messages (diff)