Hi Kannan,
I don't think Informatica will know the codes that are maintained by SAP. In my project we created a simple view based custom datasource that provided the single digit code and double digit code relation and also the texts for the languages (based on selection input).
Ideally 3 tables are involved in this conversion:
T002 - Main info for 1->2digit lang code
T002X - Language Country Information
T002T - Texts of language
So ideally you can create one more workflow for this data source and manipulate the language later on in staging.
Please let me know if it helps.
Thanks
Amit