error while using diacritical marks in matlab code in latex

Question

I'm very new to latex and I'm trying to write a latex document in polish. It contains diacritical marks such as "ą" or "ś" and it all works fine until I try to add some Matlab code to the document. My code also contains polish letters (for example in plot titles) and when I'm trying to create pdf I get a message like the one bellow for every line of Matlab code that contains some polish letters

! Package inputenc Error: Invalid UTF-8 byte sequence. See the inputenc package documentation for explanation. Type H for immediate l.80 xlabel('częstotliwość próbkowania');

Does anyone know what to do to use a diacritical mark in Matlab code in latex? Here's what I use for my MatLab code:

\definecolor{greenMatlab}{RGB}{75,150,0}
\definecolor{stringColor}{RGB}{170,55,241}
\lstset{breaklines=true,
    framextopmargin=50pt,
    frame=bottomline,
    language=Matlab,
    breaklines=true,
    morekeywords={matlab2tikz},
    keywordstyle=\color{black},
    identifierstyle=\color{black},
    stringstyle=\color{stringColor},
    commentstyle=\color{greenMatlab},
    showstringspaces=false,
    numbers=left,
    numberstyle={\tiny \color{black}},
    numbersep=9pt, 
    emph=[1]{for,end,break},
    emphstyle=[1]\color{blue},
}