Hi Johnson,
in most Connectors (e.g. SAP Java Connector or NW RFC Library) there is an API that maps an ISO Language Code (2 Chars) to the corresponding SAP Language Code (1 Char). However, I'm not sure, whether this is also available in SAP PI. Perhaps you should move this question to the Process Integration Forum: http://scn.sap.com/community/pi-and-soa-middleware
(If the question is just about "PL", then the SAP code for it is "L", but I assume you need a general solution?! If the PI system is ABAP based, you can probably use a function module like SCP_LANGUAGE_INFO.)
Best Regards, Ulrich