> The goal is to have a complete app in each location folder? 

No, just whatever matches the files pattern

> Not to have translated files with different names sitting at the same level?

I thought about this a lot.  I see some projects appending the lang to the file but if you want to translate a lot of static with a lot of languages, it gets gross fast.  This structure makes it so all you have to do is prepend "dest + lang" and your static is translated.

> But then where would non-translated files go?

Non translated would stay in your static folder (presumably alongside other static).  Ideally you should be using a default language.

> Would they be copied into each directory?

You could do this.  Simply translate everything, `**/*` and all your static would be processed.  Wouldn't recommend simply because it would take forever.  One lazy config I had working (and kinda liked) is named anything that needed translating to `somefile.i18n.ext` and then wrote my pattern `**/*.i18n.*` and all those files would be translated and added to your dest.