Oracle - some of polish characters are not display

Question

I have an app in Windows Form using Oracle Data Provider, oracle version 12c. On Windows 7 all polish characters are ok, but after migration on Windows 10 some characters are ok, but some other are displaying as strange signs, for example

informujšca

except

informująca

Characters which are not display good: ą, ś, ź

In C# I set environment:

Environment.SetEnvironmentVariable("NLS_LANG", "AMERICAN_AMERICA.EE8ISO8859P2");//POLISH_POLAND.EE8MSWIN1250");

The only answer I found on internet is parameter which is commented, but unfortunately it's not working.