Use DBD: :Oracle 1.16 to access Oracle 9.2 database

I try to connect to an Oracle 9.2 database using following code:

 my $dbh = DBI->connect($config->{dburl}, $config->{dbuser}, $config->{dbpass});

It failed with error:

DBI connect('host=host;sid=dbsid','user',...) failed: ORA-12705: invalid or unknown NLS parameter value specified (DBD ERROR: OCISessionBegin) at ..

I have to explicitly set the ENV variable NLS_LANG to make it work. The new code looks like:

$ENV{NLS_LANG}="AMERICAN_AMERICA.UTF8";
my $dbh = DBI->connect($config->{dburl}, $config->{dbuser}, $config->{dbpass});

and it works.

The initial thought is that the default NLS_LANG from DBD::Oracle has to match the server configuration which is "AMERICAN_AMERICA.UTF8". But the follwoing code works as well:

$ENV{NLS_LANG}="AMERICAN_AMERICA.US7ASCII";
my $dbh = DBI->connect($config->{dburl}, $config->{dbuser}, $config->{dbpass});

So maybe the DBD:Oracle is sending some invalid NLS_LANG string though I havn't figured out what it is.