Hi Ram
your problem is not that you cannot set the the session locale settings after the logon, but rather how the language lookup should handle non-matches and what fall-back output should be provided.
Currently SAP HANAs text join does not provide a fall-back language for incomplete data sets.
If the data is not maintained in the language that was set, then the result will be NULL.
Using a manual filter on the language denoting column is fine - really, the text join is a simplification for the modeler. Technically it doesn't do anything else then a normal join.
- Lars