the dutch language is famous, well semi-famous, for a number of things, being quite unintelligible is one example. so when something is gobbledegook you can say : it's double dutch to me. quite possibly because dutch is my first language, this seems unreasonable. have you tried making sense of finnish? or icelandic? ha ha but then you wouldn't have the alliteration and if you said double danish, for example, people might think you're talking about an especially large pastry.
but one thing dutch should be famous for is the possibility of making a diminutive version of a word by adding 'je' at the end : huis = house, so huisje = small house. (a small technical detail i'll mention because otherwise i'll be subject to the wrath of dutch native speakers since many dutch people have a hobby which is finding fault with things or with what people do and say and then very pointedly pointing out the fault that you've made : a word ends that in a vowel is a little more complicated to make into a diminutive because you have to add a consonant and possibly even another vowel, for example auto = car, autootje = small car — and also : some words only exist in the diminutive form, for example praatje = a little talk, or chat.
it can also be used intentionally or unintentionally to belittle or humiliate and one interesting use of this is in the kind of racism/colonialism that is practised here (i realise this isn't going to make me any new dutch friends) for example when my mother refers to a muslim or indonesian woman as 'een vrouwtje' — a little woman.