latex-if.tex

\documentclass[11pt,a4paper]{article}
% Declare the new flag
\newif\ifspanish
% To set the flag, now you use:
% \spanishtrue
% \spanishfalse

% To check the value, the construct is
% \ifspanish
%    Value if true
% \else
%    Value if false
% \fi
% Of course, the \else clause can be deleted as needed

\begin{document}
\spanishtrue

\ifspanish
  Esto esta en Español
\else
  Esto, sin embargo en ingles
\fi

\spanishfalse

\ifspanish
  Esto esta en Español
\else
  Esto, sin embargo, en ingles
\fi

\end{document}