Hi @FelixL,
it looks like toLocaleString is influenced by the browser but also the server location and language settings when the nodes are executed. This is why you see different results.
To force it to a specified language you can use .setLocale('de'): this will tell toLocaleString to create a human-readable string with the German formatting.
@giulioandreini thanks for the detailed explanation, now it totally makes sense why this is happening
@pemontto thanks for those env variables, good to know there is a solution for the whole instance
Will try them later – do not want to break any running workflows which maybe depend on English formatted dates right now.