Changing language RTFM theme

Hi there, I am trying to change the language of things like Search the documentation, Clear history, etc at the RTFM skeleton....I swapped the 'en' at the base.html.twig file for another of the languages listed at the languages.yaml file but nothing happens....cleared the cache and browser and still the english language remains. Is there something else I need to change to achieve this?

There are changes needed to system.yaml. Docs

Thank you very much!