I add a language to the OSCMax 2.5.3, duplicatiing languages directory: includes/languages/espanol to other, example: includes/languages/catalan, and same in admin directory, but when I select this language the catalog show white page. In forums pgmarshall white this solution for this problem:
White page = php error.
You need to go to catalog/includes/paypal_wpp/languages/espanol and copy it to catalog/includes/paypal_wpp/languages/catalan.
after this, the catalog work again.