(Korean language) "ESL" and "KSL"; what about third, fourth or fifth?

Korean Studies Discussion List brought a Korean language textbook review in my mailbook. The book is no doubt good as the review tells, but I cannot but find the continuous reference to "Korean as Second Language" quite ridiculous. It comes of course from "ESL" or "English as Second Language", as the idea of learning several foreign languages must be quite foreign. Oh but it must be the term foreign which has been replaced by the word second in this case. I still need to ask if there are any KTL, KFL or KFL textbooks or ETL or EFL courses available? Here we see the problem of making a distinction between the "fourth language" and the "fifth language": KFoL and KFiL perhaps? Or should I try suggesting that they'd say Korean as non-native language (KNNL) instead in the US?