If I knew that I would have posted how it happens.

 I've not had a single member say anything about this error, I only see them in email.

 The same word "śląskie" which I don't even know what language that is.

I personally cannot repoduce the error, I do know it is an ongoing error for months now.

Called script:
/searchKeyword.php

Request parameters:

array (  'type' => 'location_country_state',  'keyword' => 'PL',  'state' => 'śląskie',  'lang' => 'en', )