I merged en.json and nl.json via
jq -s '.[0] * .[1]' en.json nl.json > nl2.json && mv nl2.json nl.json
Which adds all missing elements in nl.json that are present in
en.json. Take care,j I believe that it keeps the sorting from
en.json (alphabetical), so it might create a bigger diff than
necessary.
Rens Oliemans