Polish characters missing/replaced with symbols

When I was making a backup of my MySQL server I noticed that letters like:
Ź, Ą, Ó, Ł, Ż, Ń
were missing. How I can fix this?

Hi Tomek_Zapalka,

To resolve the issue please let us know where exactly these letters are missing, in your backup?

Also, please let us know more details about the collation and character set that you use in your database.

Thank you and sorry for the inconvenience.