As below commenters have pointed out this is a choice. Uranium can be sourced from many locations. It can also be processed in Germany if they had wanted (Germany is a part owner of Urenco which also has a small enrichment plant in Germany amongst other locations).
To steel man your argument though in the context of funding Russia’s genocide in Ukraine when comparing Germany’s use of gas vs if it kept its nuclear plants operating we should look at the Euro per joule cost of the gas bought from Russia vs the Euro per joule cost of enriched U bought from Russia. I suspect we are talking orders of magnitude difference. But that information is conveniently not being provided in this article.
Neither is discussed the ability to easily stockpile a couple of years of fuel supply as many plants have done, which right now would enable you to continue operating while spinning up supplies from elsewhere.
Another note regarding the claim in the article: “For the operators of so-called WWER reactors, Russia is therefore even the only supplier of custom-made hexagonal fuel rods.”
Westinghouse can make these fuel assemblies, they started on this for Ukraine. Framatome I believe has also offered to do this. There’s nothing secret about Rosatom fuel assemblies.