PL/SQL Date issues with Multi-language

We are currently implementing Multi-language on Oracle 11i10 and implementing Brazilian Portuguese with South American Spanish to follow. We have problems like

Hard Coded date checks in the functions 

 

i.e.

and to_date('01-'||pabl.period_name, 'DD-MON-YYYY') between decode(substr(period_name_in,1,3), 'DEC', to_date('01-JAN-1900', 'DD-MON-YYYY'), add_months(to_date('01-'||period_name_in,'DD-MON-YYYY'), 1)) and decode(substr(period_name_in,1,3), 'DEC', to_date('01-JAN-1900', 'DD-MON-YYYY'), to_date('31-DEC-'||substr(period_name_in,5),'DD-MON-YYYY') )

and to_date('01-'||pabl.period_name, 'DD-MON-YYYY') between decode(substr(period_name_in,1,3), 'DEC', to_date('01-JAN-1900', 'DD-MON-YYYY'