如何根据当前区域设置呈现不同的部分

I got index.erb and index-de.erb, and somewhere I saw an example where this resulted in index-de being rendered when I18n.locale was :de, but i just tried and it did not work and I could not find any documentation on this subject. So does this actually work or do I need an extra plugin for this ?I got index.erb and index-de.erb, and somewhere