i18i EE JS files in directories starting with s

What does this MR do?

i18i EE JS files in directories starting with s

This is one of many MRs opened in order to improve the overall internationalisation of the GitLab codebase.

This MR only targets the Vanilla JS files.

https://docs.gitlab.com/ee/development/i18n/externalization.html

Related issue is https://gitlab.com/gitlab-org/gitlab-ce/issues/59733