\documentclass[ngerman]{scrartcl}

\documentclass[ngerman]{scrartcl}
\XeTeXtracingfonts=1

\usepackage{babel}
\usepackage{libertine}
%\usepackage{fontspec}
%\setmainfont[RawFeature=+ccmp;+locl;+mark;+mkmk;+kern;+liga;+clig;+trep;+tlig]{LinLibertine}
\usepackage[left=1cm,right=1cm,top=1cm,bottom=1cm,a4paper]{geometry}
\setlength{\parindent}{0pt}
\usepackage{eso-pic,calc,xcolor}

\makeatletter
\AddToShipoutPicture{%
\begingroup
\color{lightgray}
\thinlines%
\ESO@div{\paperwidth}{\ESO@gridDelta}%
\multiput(0,\LenToUnit{\ESO@yoffsetII})(5,0){120}%
{\ESO@Vline{\LenToUnit{\paperheight}}}%
\endgroup
}
\makeatother

\begin{document}
\section{Kerning-Test: Linux Libertine: fxl-m-n}

{\fontfamily{fxl}\fontseries{m}\fontshape{n}\fontsize{3cm}{3.2cm}\selectfont
\input{testkerning.inc}
}

\end{document}