Mongrel Nation - Brown cow

Frisian is even closer to English than Dutch. I always liked the rhyme : "bread, butter and green cheese is good English and good Fries", which in Frisian is "Brea, bûter en griene tsiis is goed Ingelsk en goed Frysk". There's a hilarious video on Youtube where the comedian Eddie Izzard attempts to talk to a Frisian Farmer in Old English and gets surprisingly far. [this video]

Your point regarding species extinction is a good one. However, in languages, "extinct language" has a more specific meaning. See [link] . I believe that language extinction occurs when it's possible to point to the last living speaker of the language, or more generally, when there is no modern version of a language. But you are right that the person who asked the question is more likely to think of the more transitional, biological meaning. You may like this clip where Eddie Izzard goes to Friesland to "buy a brown cow" in Old English. [this video]

Eddie Izzard speaking old English to a Frisian farmer: [this video] As a Norwegian who speaks English and school-German, Dutch is fairly easy to read but sounds like you're speaking a mix of English, Norse and German with a mouthful of gravel (similar to the Danish, who Norwegians like to say speaks Norwegian with a potato in their mouth)

There was a UK TV show years ago that I've always remembered where the presenter tried to buy a cow using Old English with a Frisian speaking farmer in Holland: [this video]