If you can't read German, what use is that sign? If you can read German, what use is that sign?

As a fellow German, this screams "there is a problem, here is the wrong solution" to me, too. Frequently, the wrong solution magically appears when there is a bias to enforce, so I do lean more on the racism theory.

I agree as here it also seems to be bureaucracy and a lack of funding.

The trigger for introducing the rule was an incident the previous weekend. Nobel - himself a qualified lifeguard - had to rescue a toddler from water that was far too deep. "Our lake is up to 13 metres deep in places. That is simply dangerous," [Mathias Nobel, manager of the Heidebad lake swimming area] said. What is feasible and what is not?

Nobel said children in particular needed to understand how to behave around water and had to be supervised by people who also knew how to act. Lifeguards also needed to be able to communicate with visitors directly. If a group arrived without a single person with sufficient German, he and his team had serious concerns, he said.

Maybe they need more personnel.

Differences in language are tied very closely with differences in race. Excluding people based on the language they [don't] speak is simply racism.

Safety is not a concern here. What language you speak has nothing to do with whether you know how to not drown. I'm quite certain that there are plenty of German speakers who blissfully fail to read or otherwise ignore that sign. Finally, the article seems to make it clear that the swimming area is understaffed for the number of bathers visiting. That's a staffing issue.