The term is used, in the narrower sense, to refer to speech made incomprehensible because it is a mixture of words from different languages, often mispronounced. In the broader sense, it may mean just "gibberish". Welsch is an old-fashioned word for a Romance language or a speaker of such a language. The origin of the Kauder part is not clear. The most convincing explanation, to me, takes into account that in Swiss German, the term is Chuderwälsch and may have originally referred to the speech of the people of Chur in the canton of Graubünden--Martin Luther used the term in this sense.
In any case, this is a favorite word of mine because of the way it sounds--it mimics what it designates (it will never make it into English, though, I think). I was reminded of it when we talked, in a previous post, about Denglish, the mixture of German and English found in the news, in advertising, and in daily speech in present-day Germany--language purists call it, yes, Kauderwelsch, although it's perfectly comprehensible to most.
Secret bilingual language
13 hours ago