Dear Hans and Wolfgang, Thank you for the comments and samples.

What exactly do you plan to do with the language check, for simple texts your method is overkill and labeltexts are better suited, even a command which prints a text can be written in TeX without problems:

Yes, you are right. Those methods are beyonds of my normal use. For me, either \doifelse or context.setvalue is enough to set some labels depending on two languages, Korean and English. However, it is a good oppertunity to know various methods and lua codes. I didn't know that \labeltext can do the same thing. Your sample gives me a new ideas to handle them. Thank you so much. Best regards, Dalyoung