We will be in Arhus for 1 day at the end of May. Is the Den Gamle By open air museum a worthwhile stop? Are there English explanations on signs or English speaking docents?
You can ask people working there. Most Danish people speak English, especially in larger cities.
I think it is always worth while. We visit https://www.dengamleby.dk/en/ every time we are in Aarhus - approximately once a year. As far as I remember all signs are in Danish AND English.
There are guided tours in Danish, English and German: https://www.dengamleby.dk/en/plan-your-visit/guided-tours/
Aarhus is a charming, compact city. We enjoyed Den Gamle By, the Occupation Museum, and ARoS Art Museum over our two days in Aarhus. I think it just depends on your travel interests and what else you will see on this trip.
Den Gamle By has signage in English, as do most things in Denmark. It is extensive and will take you several hours. On a future visit, I would also like to see the Botanical Garden. But one thing we liked most about Aarhus was just strolling through streets, stopping at cafes, and walking along the parks on the port.