There are issues in displaying Polish characters in Roots Magic despite using UTF character set. The issue appears wherever HTML is used as output of text. The control string I've used to test it is "ąśężźćńół", which are all the additional letters used in the Polish alphabet. Those letters are properly saved to the database when entered on edit screens and properly displayed in nearly all the fields, lists and reports as far as I could tell, but not in the HTML display fields.
This is mainly visible in the Citation Manager. After entering this text into all possible fields, you get something like:
Short Footnote: ĄA�ęA1AoćA�A3A�.
Bibliography: , ĄA�ęA1AoćA�A3A�.
Source Edit screen suffers from the same issue on the Citation tab. In order to be able to read larger portions of text, I need to actually edit the source and go into the master text and detail text tabs, reading them in the editable fields, which display those characters properly. I've seen this issue for quite some time; it is by no means new. Let me know if I need to do anything else to help you replicate and fix it. I have seen a similar issue reported and fixed for certain German characters, but not for Polish specifically, so just letting you know in case nobody else has seen it before.
Here is the link to a screenshot.