In Common errors^x, Dialects^x

O, I thought you were, as your quote is in Chinese. Yes, L(x) is a function indicating whether a language is 'native' or 'foreign' to a person. It is not restricted to Language Acquisition though, as it is widely used in such topics as Language Teaching (see for example, Eric Hawkin's...

1. She phoned to ascertain whether he were dining at the club. 2. He looked at me as if he suspected I were cheating on him. 3. If he were surprised, he didn't show it. Only my opinion; but I would call these three examples incorrect in standard English. (Some rural BrE dialects use "were"...