Add a banner to promote participation in the translation project

While exploring an option for issue #348793 (comment 830384045)

I was thinking about how we could increase community contribution to the translation project https://translate.gitlab.com/.

Maybe we could include a banner when users set the preferred language other than English, under Preferences>localization section.

The banner content would be, Hey, are you interested in contributing to the translation project? Here is the link to the project!