# MWE:

\documentclass[11pt]{book}
\usepackage{paracol}

\begin{document}

\begin{paracol}{2}

\switchcolumn[1]* \section*{Heading in Language 1}
\switchcolumn[0]  \section*{Heading in Language 2}

\begin{enumerate}
\switchcolumn[1]* \item Text in language 1
\switchcolumn[0]  \item Text in language 2
\switchcolumn[1]* \item More text in language 1
\switchcolumn[0]  \item More text in language 2
\switchcolumn[1]* \item Yet more text in language 1
\switchcolumn[0]  \item Yet more text in language 2
\end{enumerate}

\end{paracol}

\end{document}


# Output:

For some reason, only the first item is vertically misaligned, but the others are aligned. Why is this?

As Section 7.2 of paracol's manual says, \switchcolumn in an enumerate environment (and other relatives) causes problems such as you're facing, when the environment is included in paracol. One simple solution is to make paracol included in enumerate as described in 7.1. That is, the following will give you a good result.

    \begin{paraccol}{2}
\switchicolumn[1] \section{...}
\switchicolumn[0] \section{...}
\end{paracol}
\begin{enumerate}
\begin{paracol}{2}
\switchcolumn[1]* \item Text in language 1
\switchcolumn[0]  \item Text in language 2
...
\end{paracol}
\end{enumerate}

• So paracol environments can never be nested, although enumerate/itemize/etc. environments can be. thank you – Geremia Apr 13 at 19:55