The first number is lubricity (how well it flows) at cold start...
Second number is lubricity when hot....
Hence a 10W- oil is good only when the weather is above freezing.
a 5W- oil is for moderately cold, down to around minus ten (Celsius)
0W- is for very cold, below 20 Celsius (zero Fahrenheit) or cold for an extended time
On the other side...
-40 is very thick when hot, -20 is very thin when hot.
Denmark looks like my home of Virginia, snows once a year, gets a little cold, moderate summers.
Run a 5W-30 (my choice) or a synthetic 5W-40....
If it was very cold, run a 0W-20 or 0W-30...
If it was very hot, run a 10W-40 or a 5W-40