HTML response code 500 (internal server error) when logging in with pl_PL locale

I’m testing the hosted SuiteCRM ( After installing the Polish translation I cannot log in - the login form is displayed correctly but after pressing the “LOG IN” button all disappears (the page gets blank/white). Digging in debugging info I found that the server returns the code 500 to the browser.
There is no problem when logging in using us_US or de_DE locales.
I looked for some hints in the SuiteCRM’s log file, but didn’t find any errors.
What else should I do to pinpoint the problem?

Can you please download a pl_PL fresh new zip file again?
(current language pack version will state when installing)