Every module and skin keeps its own text, its language strings. A language is a full set of those strings. Jamroom comes with English (en-US). To add a language, you copy English and translate the copy.
Open ACP > Modules > Users > Users > Tools > Create a Language:
es-ES or fr-FR.Click clone language strings.
Open the Language tab of a module, choose your new language in the Language list, translate the strings and save. Do the same for each module your site uses, and for your skin (ACP > Skins > (your skin) > Language).
There's no single file with every string: each module and skin has its own Language tab.
Export Language Strings and Import Language Strings (in the same Tools tab) move a language between sites, or let a translator work offline. Reset Language Strings restores a module's or skin's original strings.
Choose Default Language in ACP > Modules > Users > Users > Global Config, in the Account section. New members get this language. Each member can change their own in their Account Settings.
To let visitors switch language with a link, add ?set_user_language= and the language code to any page address. For example, in a skin template:
<a href="?set_user_language=es-ES">EspaƱol</a>
<a href="?set_user_language=en-US">English</a>
A set of flag images you can use for language links. Put them in your skin's img directory.