I have found at When translating a site go with URLs in Chinese or English? that
The URLs should be in the same language as the content.
If you want a Chinese URL, it's pretty clear that you go with
However, I wonder how is it with European languages. Should you replace umlaute by common standards?
For example, what would be better practice, to translate example.com/product/oil
in German into
example.com/produkt/öl
or
example.com/produkt/oel