Is this language still being developed as new things are being added to the world.
They have a Navajo keyboard for mobile phones so Navajo speakers can text in Navajo, so yes, Navajo is a language very much capable for expressing contemporary concepts and things.
Speaking of mobile phones, Daybreakwarrior posted a video several years ago about how to say cellphone in Navajo: https://www.youtube.com/watch?v=PzwupgNm0GI
In German, specifically, new words are formed to meet new things or concepts by combining previously existing words. Check out this article! https://blog.oxforddictionaries.com/2015/12/09/german-compound-words/