Issue #2722265 by willito, kellyimagined, joachim, hussainweb, munizjor,...

Issue #2722265 by willito, kellyimagined, joachim, hussainweb, munizjor, selfuntitled, lisa.ugray, soulsesa, The Sean, kjl16, kurthill4: docs for MailManager::mail() refer to obsolete function user_preferred_langcode()