I can see why that would be helpful at Frankfurt airport. It's really huge and easy to find yourself in the wrong place - to get from the EU flight area to the US area you need to go through a security check point and it is confusing.
The lack of German won't be a problem though, if that is their main concern, because the signs are also in English and most people will speak English too.

My parents have gotten older and, while they can walk and do not have dementia, they are definitely not as quick or sharp as they used to be. They are traveling to Europe. The flight there is direct, but for the return, they will have to navigate a connection through Frankfurt and are concerned about getting lost/missing their connection to the US.

Frankfurt airport offers a 'guide service'. Has anyone used such a thing either for themselves or older people in their lives? It's 60€. They have 1.5h layover from a short EU flight to their US flight, assuming no delays. They don't speak German, don't travel frequently, and are a bit nervous about the hassle of travel. Worth it?