English is a Germanic language, so it's closely related to German, Dutch and varieties thereof. It's changed a lot over the years: it's got a lot of French/Latin vocabulary due to those pesky conquests, and its grammar has changed in various ways (loss of inflections, loss of case, word order changes). But Old English was much more like those German/Dutch varieties, and Friesian in particular. Of course Friesian has changed too, but not as much as English has.
So obviously Eddie Izzard is going there, armed with only a smattering of badly-pronounced Old English, to try to buy a brown cow. Why he wouldn't buy a Friesian cow (the 'classic' black and white ones) I don't know, but whatever. Anyway, he totally manages to talk to this Friesian farmer in Old English, and they understand each other. It's brilliant: