It's been covered here by people like Gokhan and others a million times, but the reason those other oil weights are specified in other countries is oil availability. Many countries don't have 0w-20 and other weights readily available or even at all. So, what are they supposed to do, run no oil?
I think Gokhan and others are wrong on that point, and I've said so whenever I see that "availability" myth. In Australia and New Zealand you can use anything from 0W16 to 15W40 in a new Toyota hybrid, and in the shops the shelves are full of all oil viscosity grades from 0W16 to 20W50, it's not for lack of choice or availability.
I just went to the Valvoline Europe web page and looked up the oil for a RAV4 Hybrid and they gave a number of recommendations including: 0W20, 5W30 and 15W40. I don't think France, Germany and England are short of quality oil.
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Sure some countries have a limited oil selection, but many are the opposite and have a good selection of oils and Toyota is happy for them to use whatever they want from 0W16 to 15W40 within cold starting ability of their climate.
OP, I vote for 5W30 in winter and 10W30 in summer, in a good name brand synthetic. Job done.