On Wikipedia, the noun Babel (in reference to the Tower of Babel) refers to the user language templates aiding multilingual communication by making it easier to contact someone who speaks a certain language. The idea originated on the Wikimedia Commons and has also been implemented on Meta-Wiki and some of the other Wikipedias, to varying extents. To participate, you can add the Babel template to your user page by following these instructions:
So, for example, {{Babel|en|de-1}} would indicate a native speaker of English with basic knowledge of German. {{Babel|en-5|sv|no-4|he-3|lt-2|es-1|da-0}} would indicate a professional proficiency of the English language, a native speaker of Swedish with an almost-native knowledge of Norwegian, advanced knowledge of Hebrew, an intermediate knowledge of Lithuanian, a basic knowledge of Spanish and no knowledge of Danish.
These templates add you to the category associated with your level of understanding, and to the overall category for that language.
To find someone who speaks a particular language, see Wikipedians by languages, and follow the links. For the most part, the two and three letter codes are taken from ISO 639, but see this list for a comprehensive guide.
You can help expand this system by creating templates for your language. Categories have already been created for most languages which have editions of Wikipedia containing over a hundred articles; they just need labelling up! It's recommended to copy the English or French versions when expanding the scheme, as most of the languages listed here are incomplete.
Note that many sign languages currently use the same template with language code "sgn", with the exception of American Sign Language users who should use the American Sign Language template. Other sign languages can be specified within the {{User sgn}} template itself. The use of this parameter requires the user to perform an extra step when using the {{Babel-#}} templates, described here.