Make a copy of the language file data/language/de.json and rename the file with two characters to a new language file:
Spanish: es.json
French: fr.json
Danish: dk.json
Dutch: nl.json
etc.
Translate all words starting from the colon in each line:
{"SAVE":"archivo","CLOSE":"cerca",...}
Open Explorer in the web interface of Brautomat. Copy the new language file to the /language folder on your Brautomat. Finally, the new language file must be made known to Brautomat: edit the file /lang.js