Monolinguist, English-only speakers often refer to people who don't speak English natively as "ESL" or say they are learning a "second language". More often than not, this is not true, as many people are multi-lingual with 3 or more languages
It makes false assumptions about English learners, centres English as the "default" or "expected" first language, ignoring that many people learn multiple (>3), non-English languages first.