MWE:
\documentclass[17pt,a4paper]{extarticle}
\usepackage{graphicx}
\usepackage{fontspec}
\usepackage{polyglossia}
\usepackage{soulutf8}
\setmainfont{LMR12R-Gregory}
\setdefaultlanguage[variant=american]{english}
\setotherlanguage{russian}
\setul{}{2pt}
\begin{document}
\ul{Привет}
\end{document}
Output (it's the tiny vertical line in the picture):
Is there a way to make this work as one would expect?
