sinatra-r18n

https://github.com/r18n/sinatra-r18n

A Sinatra extension that provides i18n support to translate your web application. It is just a wrapper for R18n core library. It has nice Ruby-style syntax, filters, flexible locales, custom loaders, translation support for any classes, time and number localization, several user language support, agnostic core package with out-of-box support for Rails, Sinatra and desktop applications.