Polish language handling in MondoSearch
MondoSearch relies on the language handling on Windows Server to handle languages that are not default to the Windows installation. Therefore, you must be sure that the Chinese Simplified and and Chinese traditional language packs for windows are installed on the server.
Then, in the insite, under CRAWLER SETUP > HOSTS > Languages, you can set the languages to be recognized. By default, all supported languages are set.
default search page (on your site) is only submitting the search to return results in English and French. The input parameter in the form on the page should be set to PL instead of EN for you to return the Polish results.
You can see in the parameters passed that there is one called EN=X if you add &PL=X or change EN to PL, you should be able to search for the Polish pages.