This is the multilanguage.sty package for LaTeX
The solution is based upon TEX StackExchange answer by Riccardo. Apparently, this user prefers to keep an air of mystery.
Usage:
% MULTILINGUAL SUPPORT
%enables babel to every lang supported by your document
\usepackage[italian,english,lithuanian]{babel}
\usepackage{multilanguage}
% set short and long language codes. The second one must be known by babel
%\setdoclang{it}{italian}
%\setdoclang{en}{english}
\setdoclang{lt}{lithuanian}
% END MULTILINGUAL SUPPORT
...
% Sections, subsections, subsubsections: in the first parameter you can freely use both short or long language codes
\sectionlang{it}{Sezione 1}
\sectionlang{english}{Section 1}
% Strings that are displayed only in a certain language
\lang{it}{Questa stringa appare solo in italiano.}
\lang{en}{This string shows up only in English.}
\lang{lt}{Ši eilutė bus tik lietuviškame tekste.}
% When you have only two languages, you can simply rely on this if-else construct
\langif{it}{If vero: questo e' italiano.}{Else: this is for any language different from Italian.}