How to create a page with two columns that can span pages to achieve my special goal?

Question

I am a Chinese plain TeX user and also a beginner. Now I encounter a hard question, that is

I must write some numbered English paragraphs at the left column and its corresponding Chinese translations at the right column which have the same number with the English one. The first lines of the English paragraph and its corresponding Chinese translations should be located at the same horizontal line.

Here is an example if I can't explain this question clearly:

My method to solve this problem is using \halign with two \vtop, but it can't span pages or produce overfull, underfull \vbox.

\newcount\mycount
\mycount=1
\bigskip
\halign{\tabskip=.5in
        \vtop{\hsize=3in\noindent\number\mycount.\enspace#}&
        \tabskip=0pt\vtop{\hsize=3in
        \noindent\romannumeral\mycount.\enspace#\global\advance\mycount by1}\cr
        ...}

so ugly it is :-(

Anyone else has a better solution?

Answer 1

You may be interested in parallel package.

\documentclass[a4paper]{article}
\usepackage{parallel}
\usepackage{lipsum} %% dummy text
\usepackage{microtype} %% Just for my taste
\usepackage{enumitem}
%%%--------------- set a newlist for english--------------------
\newlist{eng}{enumerate}{1}
\setlist[eng]{align=left,itemindent=2.5em,leftmargin=0pt,
rightmargin=.51\textwidth,label=\textbf{\arabic*.}}
%%%--------------- set a newlist for chinese --------------------
\newlist{chin}{enumerate}{1}
\setlist[chin]{align=left,itemindent=2.5em,leftmargin=.51\textwidth,
rightmargin=0pt,label=\textbf{\roman*.}}
%%----------------------------------------------------------
\begin{document}
\begin{Parallel}{.49\textwidth}{.49\textwidth}
\ParallelLText{%
\begin{eng}[series=english]
\item \lipsum[1]
\end{eng}
}%
\ParallelRText{%
\begin{chin}[series=chinese]
\item \lipsum[2]
\end{chin}
}%
\ParallelPar
\ParallelLText{%
\begin{eng}[resume*=english]
\item \lipsum[3]
\end{eng}
}%
\ParallelRText{%
\begin{chin}[resume*=chinese]
\item\lipsum[4]
\end{chin}
}%
\ParallelPar
\ParallelLText{%
\begin{eng}[resume*=english]
\item \lipsum[5]
\end{eng}
}%
\ParallelRText{%
\begin{chin}[resume*=chinese]
\item\lipsum[6]
\end{chin}
}%
\ParallelPar
\ParallelLText{%
\begin{eng}[resume*=english]
\item \lipsum[7]
\end{eng}
}%
\ParallelRText{%
\begin{chin}[resume*=chinese]
\item\lipsum[10]
\end{chin}
}%
\end{Parallel}
\end{document}

Answer 2

This is why you should switch to LaTeX, my friend :)

EDIT: I only realised mid-coding that the OP required a plain-TeX solution, but I (cheekily!) decided to post my LaTeX solution anyway. There may be more elegant solutions than mine but who knows? My solution might be useful to some...

\documentclass{article}

\usepackage[showframe]{geometry}
\usepackage{etoolbox}
\usepackage{enumitem}

\newtoggle{morethanoneparagraph}
\togglefalse{morethanoneparagraph}

\newcommand{\mycolumnwidth}{0.45\textwidth}

\newenvironment{engchin}{%
    \newcommand\nextpart{%
        \end{enumerate}
        \end{minipage}
        \begin{minipage}[t]{\mycolumnwidth}
        \iftoggle{morethanoneparagraph}{%
            \begin{enumerate}[label=\roman*,resume*=chin] 
                \item
        }{%
            \global\toggletrue{morethanoneparagraph}
            \begin{enumerate}[label=\roman*,series=chin] 
                \item
        }
    }
    \begin{minipage}[t]{\mycolumnwidth}
    \iftoggle{morethanoneparagraph}{
        \begin{enumerate}[resume*=eng] 
            \item 
    }{
        \begin{enumerate}[series=eng] 
            \item 
    }
}{
    \end{enumerate}
    \end{minipage}
    \vspace{\baselineskip}
}

\begin{document}

\begin{engchin}
hello a a a a a a a a a a a a 
hello a a a a a a a a a a a a
hello a a a a a a a a a a a a
hello a a a a a a a a a a a a
\nextpart
world
\end{engchin}

\begin{engchin}
hello
\nextpart
world is flat
a a a a a a a a a a a a
a a a a a a a a a a a a
a a a a a a a a a a a a
a a a a a a a a a a a a
\end{engchin}

\end{document}