prius 2009 germany imported

I would go by what is in the owners manual. Compare the temperature variables for your location to what is in the manual and go by what is listed there. Pay attention the API classification of the oil also. That should be in the manual in the same area where the weight (viscosity) is called out.

Here in the USA the oil is marked with markings like SM along with ILSAC numbers (API classification). Confirm whatever oil you purchase meets or exceeds the API classification of oil that is called out in the manual. I am unfamiliar with how oil is labeled outside of the USA therefore the API classification may not apply in your location.

Petroleum Quality Institute of America

ILSAC Oil Specifications - oilspecifications.org

I would expect that 0-20 would be Ok and that 5-20 or 5-30 would work also.

Enjoy your new to you Prius and "Welcome to Prius Chat"!

 

The oil viscosity recommended by Toyota for North America 2G Prius is 5W-30.

I agree with the suggestion that you can follow the recommendation in your owner's manual, considering the highest ambient temperatures expected in your area.

The engine oil cap may have a viscosity recommendation printed on it. Is this true with your car?

 

If you have imported the car to Germany the oil recommended within the EU is 0w20, and the oil change interval is 10,000 miles or 12 months.
The handbook goes further and states if any other oil is used, it should only be used for 5000 miles and then 0w20 should be used.
PC member Grumpy Cabby used a gen3 Prius as a taxi. He found the fuel consumption increased very noticeably if oil other than 0w20 was used.
I also have noted this on my 2008 gen2 that also has 0w20 listed in the handbook and on the filler cap as the oil of first choice.

John (Britprius)