The detail page always uses the English "title" field content to generate the URL, e.g. http://website-test.magnolia-cms.com/author/demo-features/de/modules/shop/productDetail.Fahrräder.CATEGORY.Bicyles.Corratec-XVert-Expert-Disc-Hardtail-Bike-2009.PRODUCT.69515.html

Here you can see that we use the German "Fahräder" for the Category, but we use "Corratec-XVert-Expert-Disc-Hardtail-Bike-2009" instead of the German data I have defined for this product.

Please ensure that when we serve localized content, we also use it in the URL.