Localizations can be found here: https://github.com/ushahidi/Ushahidi-Localizations
To add a language, copy the language folder you need in your application/i18n directory (NOT the system/i18n directory). Ushahidi will automatically pick up the new language and include it in the language switcher drop down and admin language settings options. If it doesn’t show up right away, go into your application/cache directory and delete the files there.
Then you can go to http://Your_Ushahidi_site/index.php/reports?l=hy_AM for example if you installed Armenian language.
The default language can be selected on the site settings page (/admin/settings/site)
(Based on info from the forums)
We've documented a list of tips for developers and themers adding text to the platform here