In order to have Polish language spell checking In PhpStorm you must generate .dic file with words.

You can do that using linux command:

You can also download this file generated by me, by clicking: Polish PhpStorm dictionary

Next you go to settings, for single project or you can also set it as default (default setting wouldn’t apply to old procjects). Type in search “Spelling” change tab to “Dictionaries”, click + button to add folder where generated dictionary is placed. Apply. If not working, try to reboot PhpStorm.