I guess your question mostly relates to SEO value, not how to technically do it in Magento. So we are just talking about semantics here. The language prefix already makes the URL unique, plus it uniquely identifies the language for that page. So this already is a plus for SEO.
Having an additional "news-de" would not be necessary - the language is already specified and the "-de" suffix does not tell anything new about the "news" part either. Because it is unneeded, it is actually bad practice to add it in there.
A URL like "/de/nachrichten" would be making much more sense: The "news" is translated into German ("nachrichten") and this not only points out to searchbots which language is used: It also gives added value to German readers. However, it would only make sense if the actual page itself (so the German translation of some product) actually is German.
In short: Try to use an URL key that directly matches the product name that is used on that page.