Currently, the URL inside the href attribute of the <a> HTML element, that redirects the user to Content Translation for the ULS missing languages entrypoint, doesn't include any campaign URL parameter.
However, this URL parameter is needed for the entrypoint to be properly instrumented, and should be added. The event_source that should be used for this entrypoint is content_language_selector.
Screencast of the missing campaign URL parameter from production wikis: