\documentclass[ngerman,british,american,a5paper]{article}% british,american
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{babel}
\usepackage[autostyle=true,autopunct=true]{csquotes}
\begin{document}
\textquote{Hi}, he said. I like \textquote[][.]{the Iliad}.\\
\textquote{Hi}, he said. I like \textquote{the Iliad}.\\
Expectation: \enquote{Hi,} he said. I like \enquote{the Iliad.}
\selectlanguage{british}% british
\textquote{Hi}, he said. I like \textquote{the Iliad}.
\selectlanguage{american}% american