how to get the user logon language for current session?

hi,

i want to retrieve the log on language information for certain user and exactly for current session. I tried to use the FB "BAPI_USER_GET_DETAIL" to get the log on language, But this so called "logon Language" is not for the current session. It is fixed value which is configured by user. This field is option and not all user have maintained this information.

I would very appreciate if someone give me hand to overcome this problem.

Thanks.