Use getenv method instead of osl_getEnvironment.
Delete rtl and std namespace identifier
Use OString every possible place to decrease
OString<->OUString conversions.
Add some block to minimize scope of local variables
and add comments to make clear each block task.
Move propex "en_US exist in file name" check to
localize to save some extra process time.

Change-Id: I9a0455f7524f71e34efe4d32998d2d21601f14e1