Krdytkyu

Before I start, I want to say that I have already read this post and this post

I am writing a paper in two languages. I want to write other language version of every paragraphs and title just below the original version.

Is the any two switch two language by using same options like

Lang == Esp



if{Lang=Eng}

   chapter{LITERATURE}

elif

   chapter{LITERATURA}

or

if{Lang=Eng}

   {I love you.}

elif

   {Te quiero.}

Is there any way to do that?

You could use an approach like the following, I use it to create various versions of a CV document.

documentclass{minimal}



usepackage{ifthen}

newboolean{somevariable}

setboolean{somevariable}{false}



begin{document}



ifthenelse{boolean{somevariable}}{Text if somevariable is true.}{Text if somevariable is false.}



end{document}

There's always docstrip, which lets you distinguish one code from another using special comments (called guards) and also have code which is common to both.

In my opinion, the advantage of this method over the conditionals is that it's fairly simple to add more languages avoiding the hassle of nesting conditionals.

For instance, you can have a source file (let's call it source.dtx, but any other name will do):

documentclass{book}

begin{document}



%<english>chapter{LITERATURE}

%<spanish>chapter{LITERATURA}



%<*english>

emph{The Tau Manifesto} is dedicated to one of the most important numbers in

mathematics, perhaps emph{the} most important: the emph{circle constant} relating

the circumference of a circle to its linear dimension. For millennia, the circle has

been considered the most perfect of shapes, and the circle constant captures the

geometry of the circle in a single number. Of course, the traditional choice for

the circle constant is $pi$--but, as mathematician Bob Palais notes in his

delightful article ``$pi$ Is Wrong!'', $pi$ emph{is wrong}. It's time to set

things right.

%</english>



%<*spanish>

emph{El Manifiesto de Tau} está dedicado a uno de los números más importantes en

matemáticas, quizás emph{el} más importante: la emph{constante de círculo} que relaciona

la circunferencia de un círculo con su dimensión lineal. Durante milenios, el círculo ha

sido considerado la forma más perfecta, y la constante del círculo captura la

geometría del círculo en un solo número. Por supuesto, la elección tradicional para

la constante de círculo es $pi$--pero, como señala el matemático Bob Palais en su

artículo encantador ``$pi$ Is Wrong!'', $Pi$ emph{es incorrecto}. Es hora de arreglar las cosas.

%</spanish>



end{document}

(sample text taken from here and Google-Translated to Spanish)

then you only need a so-called “installation file”:

input docstrip % Loads the docstrip program

% Optional switches

askforoverwritefalse % Allows it to overwrite older files without asking

keepsilent % Reduces verbosity

nopreamble % Removes preamble

nopostamble % removes postamble

% Separating sources:

generate{%

  %

  file{english.tex}{%

    from{source.dtx}{english}%

  }%

  %

  file{spanish.tex}{%

    from{source.dtx}{spanish}%

  }%

  %

}

% Exiting

endbatchfile

which will generate an english.tex file from the parts that are marked as <english> in the source.dtx and another one called spanish.tex from the parts marked with <spanish> in the source.dtx. The parts of the source.dtx which aren't marked go to both output files.

To execute this you only need to run TeX on the installation file:

> pdftex installation.ins

The generated english.tex will look like this:

documentclass{book}

begin{document}



chapter{LITERATURE}



emph{The Tau Manifesto} is dedicated to one of the most important numbers in

mathematics, perhaps emph{the} most important: the emph{circle constant} relating

the circumference of a circle to its linear dimension. For millennia, the circle has

been considered the most perfect of shapes, and the circle constant captures the

geometry of the circle in a single number. Of course, the traditional choice for

the circle constant is $pi$--but, as mathematician Bob Palais notes in his

delightful article ``$pi$ Is Wrong!'', $pi$ emph{is wrong}. It's time to set

things right.





end{document}

You can use the iflang package:

documentclass{article}

usepackage[english,ngerman]{babel}

usepackage{iflang}

begin{document}



IfLanguageName{english}{This is english}{This is not english}



IfLanguageName{ngerman}{Das ist deutsch}{Das ist nicht  deutsch}



selectlanguage{english}



IfLanguageName{english}{This is  english}{This not english}



IfLanguageName{ngerman}{Das ist deutsch}{Das ist nicht deutsch}



end{document}

The comment package makes it easy to define arbitrary throw-away environments:

documentclass{article}

usepackage{comment}





% define comment sections that are either included or excluded 

excludecomment{ENG}

includecomment{GER}



begin{document}



begin{ENG}

  In the beginning was the Word, and the Word was with God, and the Word was God.

end{ENG}



begin{GER}

    Am Anfang war das Wort und das Wort war bei Gott und Gott war das Wort.

end{GER}



end{document}

If one defines both environments with includecomment, both will become part of the output.

Technically, this comes close to the docstrip approach suggested by Phelype Oleinik as the excluded sections are actually gobbled (lexically thrown away), that is, not compiled by the tex compiler.

You can do it quite smoothly using ConTeXt, another TeX engine. It has a mode option that you can pass as an option. When compiling with mode=thismode, everything enclosed in the proper startmode[thismode] stopmode pair will be interpreted.

Here is a MWE

startmode[english]

language[en]

stopmode

startmode[espanol]

language[es]

stopmode



starttext

startmode[english]

I love you

stopmode

startmode[espanol]

Te quiero.

stopmode

stoptext

Paste this MWE in mwe.tex and compare the output of context --mode=english mwe.tex and context --mode=espanol mwe.tex. If you want to have the two texts next to another, context --mode=english,espanol mwe.tex will do it.