Error localization (with diacritic mark)

[Mariusz]

Error localization (with diacritic mark)
Hello
I locate the app.php file for the admin panel. However, when I use Polish, they knew diacritics (ą, ć, ę, ł, ń, ó, ż, ź). the entered text disappears (see image 1). When I use alternative English characters (a, c, e, l, n, o, z) the text is displayed (picture 2). For an obvious reason, I need to set the code page and / or appropriate fonts for the correct display of names and descriptions in Polish. Please help.