Assign value to ocrd, langcode

Hello everyone

I try to assign a language code to a new business-partner, depending on where he lives. F.e. user enters 1200 for CH-Geneva, programm consults a table with zip-codes and gets "Geneva" for city name and "22" for french. City name works well, but combobox language-code can't be changed. I always get an error message:

if I use ComboBox.....Value = "22"; error is "Valid Value - Value does not Exist 66000-62".

if I use ComboBox.....Selected.Value = "22"; error is "Not allowed when the ValidValue is already loaded in SAP"

My question: Is it possible to assign another language-code to this combobox (combobox contains all necessary languages)? If yes, how to do it?

Thank you so much in advance for your help!!

Fritz