Adding multi-lingual support
You can set the language for the document using the babel package. This package manages language-based typographical (and other) rules as well as hyphenation patterns for a wide range of languages.
You can select a single language to be supported or several languages in which case you can switch from one language to another within the document as required.
The package babel uses configuration files that provide the detail of what has to be done for each language.
Monolingual support
In the following example, only US English is selected.
%% Use US English
\usepackage[english]{babel}
Multi-lingual support
In the following example, German and US English are selected.
%% Use German and US English
\usepackage[ngerman,english]{babel}
More details on the babel package are available here.