Polish letters are part of the ISO8859-2 character set, which is not supported by WorldConnect (it uses ISO8859-1, the standard "Latin" character set).
The character set (ISO8859-1, ISO8859-2, UTF-8, etc.) only matters when the characters are represented with binary character values, which is normally the way characters or symbols are represented digitally.
But HTML has a special method to access any character in a font's repertoire, no matter what the character set is for the page. It's the HTML Character Entity feature, whereby a string of letters or numbers following an ampersand can be used to indicate whatever character or symbol is desired. Here's a page listing the current definitions:http://dev.w3.org/html5/html-author/charref
The character in which you are interested is the Lstrok character (html text Ł).
The entity names are case sensitive. For example, Lstrok is different than lstrok, which is, of course, the lower case "l" with a slash.
So if you don't mind having HTML character entities in your notes text, then this is the way to go.
Note: this will NOT work in the name field. You still have to use the non-slash version there. This only works in the notes field to shorten your explanation.