A CB Language plugin is installed using the CB Plugin Manager and not the Joomla installer.
Language projects for Community Builder, CB GroupJive and CBSubs exist on our forge area, on transifex and we also have dedicated language forums for each active language team:
So if you want to help localize our scripts you can participate in an existing language team or if your language team does not exist you can start it and become its manager. If you do not see your specific language in these areas then consider applying for the position.
More resources about language plugins are available in the CB Language Plugins FAQ article.
If you are looking for the latest released language plugin for your language you should visit the Community Builder Language forge area, find the specific language sub-project and click on its link and then click on the Files tab to find the latest CB 2.0 language plugin released. These release are automatically built from the transifex projects based on available translations, so if the translations are incomplete the plugins will be incomplete.
For your convenience here are direct links to Language forge areas that have CB 2.0 Language plugins: