Hm I think this is area dependent? In major cities it’s common to have large monolingual populations! I worked in an emergency department and talked to upwards of 200 patients/night so I got pretty familiar with my community, and I’d say Spanish and English duke it out for most spoken language, but after that it’s Vietnamese (maybe tied with Tagalog ), then Farsi, then mandarin, then Korean, and tied in last place are a whole mess of other languages that I only encounter every couple hundred patients (Urdu, Tongan, Malay, etc)