I would like to ask if a native German speaker can understand a Dutch speaker with fluency or at least to have a normal conversation
I tried to rephrase those various comments and aspects (which I can agree on based on my own experience) from above into a single summary, hoping to come to an answer we can all agree on:
- Without any practice, German native speakers usually only occasionally understand Dutch words, and therefore cannot follow the topic. However, in some cases, they may make out the general context. This is comparable to the situation when Germans coming from the southern regions listen to German dialects from the northern regions.
- Spoken words appear to be similar, but the pronunciation is still different in several aspects. The similarities, however, may help to extend the comprehension. Grammar does not differ much - so, it also does not provide a major hurdle.
- There are many "false friends", as discussed in several comments, for instance by @cp or @Stephie.
- The knowledge of some German dialects (especially from the north/north-west) may assist the understanding significantly.
- The knowledge of English by the German listener may improve the understanding to a certain extent as well.
- Still, in practice it is very unlikely that no communication between these two is possible: This is, however, mainly based on the fact that either the Dutch also is able to speak German, or both are able to speak English.
My own experience
I am a native German speaker from Baden-Wuerttemberg (south-west part of Germany) and was on vacation for two weeks in Noord-Holland. Without any experience it was virtually impossible for me to understand spoken Dutch (coming from "below the Maine River", you can be sure that my local dialect was not able to help me). However, some words sound familiar, but appear to be partly spoken with a very hard and sometimes with a very soft pronunciation:
- the "ch" (see also https://en.wikipedia.org/wiki/Ch_%28digraph%29 ) sounds very hard, similar to the sound in Scottish "loch".
- due to the many "e" and "i" sounds, which are pronounced brightly, however, the language partly is also perceived to be spoken softly.
In any case, however, it is way too little to get the full context. Reading Dutch is a bit better, if you know some rules of pronunciation, e.g.
- the German "sch" often appears to be simply replaced by an "s"
- "ij" is pronounced similar to the German "ei".
By this, you easily get from the Dutch "snijder" to the German "Schneider", which is "taylor" in English.
(A good discussion on these effects is also available at https://de.wikipedia.org/wiki/Niederl%C3%A4ndische_Sprache - unfortunatly only in the German version of the article).
After two weeks in the Netherlands, on the other hand, it was easy to understand more, but still impossible to have a fluent chat. For instance, after roughly one week there, I wanted to get in contact with the local bird conservation organisation to report some sighting and thus opened up their NL-only website. I could easily understand some of the sentences written there, but there were many more, where there was clearly no chance to comprehend them without help (and this was not just due to technical terms used there).
For a German speaker, Dutch sounds familiar, and it can be possible to get an idea of what someone is talking about, but it is not readily intelligible, neither spoken nor written. Some practice or acquaintance with Low German dialects will be helpful however, and it is also true that German dialects spoken in Germany are also not intelligible to all German speakers.
To answer this question, we can look at the history of High German.
High German is an invented language. It was created as a lingua franca to facilitate communication among speakers of different, mutually unintelligible German dialects.
High German was created from Middle and Upper German dialects (which is why it is called "high" German). Because of this, speakers of these dialects find High German more easily comprehensible than speakers of Low German dialects, who have to learn it almost like a second language.
This caused speakers of Low German dialects to take on High German as their everyday language and the Low German dialects to mostly die out. This is the reason, why e.g. in Hannover the purest High German is spoken – because there is no longer any dialect there to "pollute" it.
This development only took place within the borders of Germany, not in the Netherlands, where Low German dialects were spoken, too, but High German was not used as a lingua franca. For that reason, the Netherlands have retained their dialects, which, like the Low German dialects that once existed within German borders, are just as unintelligible to speakers of High, Middle, and Upper German.
If Dutch were easily intelligible to speakers of High German, then the Low German dialects would still be spoken everywhere in northern Germany today.
No, not in practice. By default, German speakers understand only occasional Dutch words, phrases in context, most written signs and the gist of simple texts like Wikipedia articles.
It depends less on the inherent distance of the languages - about the same as to Swiss dialects - and more on other variables: how much Dutch has one been been exposed to (and how much English, Frisian and French), whether the Dutch is written or spoken, what the topic is and situation are, how much background noise there is... And last but not least there are some delicate questions of attitude and intra-European protocols.
Those context variables are why the Dutch are usually much better at German than the Germans at Dutch. Smaller peoples are doomed to be more talented. Some German may report that he communicated with a Dutchmen, but that was only because the Dutchman was desperately re-activing the German he learnt in school, and due to the accent and other mistakes, the German thought that it was Dutch that he was understanding.
If a German from Transylvania were trapped on a desert island with a truly monolingual Dutchman - a rare species - they would understand each other within days to weeks, for the purposes of life on the island. After a year or so they would be speaking some sort of Platt or Kölsch, the exact mix would depend on their personalities.
But until then... Dutch is as effective at encrypting communication from German speakers as French is.
Dutch people mostly understand Germans - although without practice they don´t speak German. Germans on the other hand need practice to even understand Dutch, since it involves many different ways of pronouncing similar words.
But if you have spend some hours studying the two languages you realize that they´re effectively so closely related, they´re almost the same language. If you took Frisian (North-western German dialect) and added some English to it you´d get something very, very similar to Dutch.
I speak German and 3 other languages fluently (French, Luxembourgish, and English) and I think, as a German, it is possible to communicate with a Dutch person. It will be a bit difficult to understand everything, but if the Dutch person speaks not that fast and makes some according hand gestures to improve the understanding, it will definitely be possible for them to communicate. There are many words which sound the same. Same thing goes for all the languages that I speak; they are all connected, with many words sounding similarly, and the syntax can be similar too at some points. This means that the sense of a sentence will be easy to understand but to understand each word will become very difficult.
In my experience, it works better one way than the other.
I can understand "a little" Dutch using my knowledge of German. For instance, I can "map" ik to ich or water to Wasser.
But if I tried to speak or write using my knowledge of German to reproduce the Dutch words, I couldn't. Meaning that a Dutch person would not be able to understand me unless s/he had a knowledge of German.
Even on the "understanding" side, it would be hard for me to understand a normal conversation in Dutch, using knowledge of German. I might be able to understand a "basic" conversation in Dutch, at the A1, or at most. A2 level on the CEFR scale. This is even though I (an American, non-native speaker), can understand a normal German conversation.
My grandmother was from a village near Weilburg in the Hesse province, central west Germany, more or less between Frankfurt and Bonn. She spoke hoch Deutsch and a village dialect that was a type of platt Deutsch, e.g., "Guh moy-yeh" for "Guten Morgen". She was born in 1902, and the highest grade she went to was 8th grade, so she was no great language scholar, but she said Dutch was easy for her to learn. In the 1920s, she was a governess of two small children in Holland. She told me she learned Dutch in about a month.
We lived for some time in Belgium, and my parents were able to communicate to some extent with Flemish people.
I can read, with some difficulties and some dictionary lookups, articles on the Dutch Wikipedia about simpler topics.
Dutch and German are NOT mutually intelligible 'out of the box', compared to e.g. Czech and Slovak. As has been mentioned a few times, some words and phrases can be understood without much difficulty, if spoken leisurely and pronounced with care. A unilingual Ducthman and a like German speaking as they normally would (speed, pronunciation, volume ...) could not even talk meaningfully about the weather, let alone polemicize about the latest political events. Vocabulary is about 30% similar (if exactly so, the percentage drops to maybe 10%), pronunciation of like vowels, consonants and/or diphtongs often differs greatly and grammar only rarely helps in aiding mutual intelligibilty.
I speak as a native Dutch speaker from Flanders (Belgium) and as a university-trained language teacher speaking Dutch, German, English and French fluently, having a smattering of Spanish, Italian and Swedish. No bragging on my part, only underpinning my claim that I consider myself well-placed to offer this brief opinion on the subject. Fact remains that both languages are closely related, as both also are to English, Frisian, Danish, Swedish, Norwegian and Icelandic (the other Germanic languages).
Mutatis mutandis, the almost exact same can be said of the equally closely related Romance languages, to wit: French, Italian, Spanish and Portuguese (Romanian, however, due mainly to its geographical position more to the east of the European mainland, and therefore more influenced by its surrounding Slavic neighbours, is a lot more tenuously related to its Romance brothers). Going a bit further back in time, even Germanic, Romance and Slavic languages are related to eachother, as even a quick and cursory comparison between some basic vocabulary items reveals. Unravelling the linguistic mists of time still more, even a family link can be established between aforementioned language groups and the Indian Sanskrit. This is also why linguists talk about the Indo-European family of languages.
My father, who came from Oldenburg, Niedersachsen spoke Plattdeutsch. He told me that Platt speakers could converse with Dutch people without any problem. He, however warned me never to tell a Dutch person that Plattdeutsch was similar to Dutch. I was about 7 years old when he told me that. When I was 36 years old, I was on my honeymoon. We were in a small hotel in a small village near Mainz. there was a Dutch couple having dinner at a table next to us. Towards the end of our meal, I mentioned to the couple that my father was from North Germany and that he spoke Plattdeutsch and that Plattdeutsch was very similar to Dutch. With that the couple got up and left the room. I guess my dad's admonition some 30 years later was still true