[Tex/LaTex] Beamer presentation not showing amsmath symbols an german characters

amsmathamssymbbeamergerman

I'm curently working on an beamer presentation including equations. My problem is, that there aren't any amsmath symbols shown. The code is compiled without any error. Here are the used packages I identify as relevant:

\usepackage{polyglossia}
\setmainlanguage{german}
\usepackage{fontspec}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{mathtools}
\usepackage[math-style=ISO, bold-style=ISO, sans-style=italic, nabla=upright, partial=upright]{unicode-math}
\setmathfont{Latin Modern Math}

The header is bascily an modified version of my normal COMA-class header, where all amsmath-symbols are working like a charm.
Second problem is, that there are no german-special-characters like ä, ü, ö, ß shown if I use them directly. I have to type them manualy (\ss etc.).

Thanks in advance.

Edit: A small demonstration. \rho and \approx are not displayed in the .pdf, same with the umlauts.

\documentclass{beamer}
\usepackage{polyglossia}
\setmainlanguage{german}
\usepackage{fontspec}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{mathtools}
\usepackage[math-style=ISO, bold-style=ISO, sans-style=italic, nabla=upright, partial=upright]{unicode-math}
\setmathfont{Latin Modern Math}
\usetheme{default}

\begin{document}
\maketitle
\frame{
\frametitle{Inhalt}
Lorem ipsum....
\begin{equation}
\rho \approx \frac{M}{V}
\end{equation}
Some umlauts: ä ö ü ß 
}
\end{document}

Best Answer

The umlauts should work if your file is correctly encoded in utf8.

For the math symbols you must use the professionalfonts theme if you want to use unicode-math to avoid that beamer resets the math fonts.

\documentclass{beamer}
\usefonttheme{professionalfonts}


\usepackage{polyglossia}
\setmainlanguage{german}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{mathtools}
\usepackage[math-style=ISO, bold-style=ISO, sans-style=italic, nabla=upright, partial=upright]{unicode-math}
\setmathfont{Latin Modern Math}


\begin{document}
\maketitle
\frame{
\frametitle{Inhalt}
Lorem ipsum....
\begin{equation}
\rho \approx \frac{M}{V}
\end{equation}
Some umlauts: ä ö ü ß
}
\end{document}
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