User Environment Language is not setting up dynamically with ARP_RAXINV_MLS_FUNCTION

Hi,

In 11i custom program "Print Selected Invoices (BI)", user environment langauge is coming up dynamically based on invoice number where as it is giving only "US" irrespective of invoice number.

I have identified below statement which is giving different language codes in 11i where as it is giving only "US" in R12. because of this I am not getting invoice numbers in output file.

Please help me to overcome this.

select userenv('LANG')
from   dual;

Thanks

Siva