On Special:ContentTranslation page,
Mixed Content: The page at 'https://es.wikipedia.org/wiki/Especial:ContentTranslation' was loaded over HTTPS, but requested an insecure XMLHttpRequest endpoint 'http://cxserver.wikimedia.org/languagepairs'. This request has been blocked; the content must be served over HTTPS.
ContentTranslation likely to not work without https here.