Just after I installed polish translation Mail merge stopped work and there was a fatal error during browse/add database file
Please don’t copy the question but give more information. What do you mean with “Polish translation”? Quite often, it’s important to tell what OS and what version of LibreOffice you have. Better tell that right away. It’s better to give more information than needed than too little.
macOS Catalina, the newest LibreOffice 7.0.3. Polish translation means Polish translation 
polish language package. When I change language from Polish into English Mail merge works ok. But with polish language crashed every time.