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
Every language is constantly changing to adjust to the experiences and thought of the people. For example, in indigenous Guiana, the -koana instrument suffix is becoming more popular to express technology.
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/