Hi Bert-Jan,
Apologies aren’t necessary, we all started with nothing, right?
Indeed, the ¨NL Omschr." tag is from an other program
(there’s several weather apps you can install for extended weather info, like OpenWeather, Buienradar, Buienalarm, KNMI).
But Temperature is provided by the native/onboard/built-in “Weather” (“Weer”) tags.
As you can see, I can select it
Homey also provides for a Weather description as you can see (no apps needed):
When your Homey’s language is set to Dutch, enter ‘weer’ into the search bar 
