为什么德语总是被黑成是发音最难听的语言？

I speak 3 of those languages fluently: German as mother tongue, French every day (I live in France since 8 years, my wife is half French, half Spanish), and I lived a year in Spain.

You might say: Since German is your mother tongue, your opinion doesn't count. But I will still give you a few reasons why I think that German is not the most difficult in pronunciation, and what Carlos I really meant:

I am no linguist by training (I am mechanical engineer). But logically, a language is hard to pronounce if

1. It contains sounds which are hard to pronounce for a foreigner. Apparently, we learn as babies inadvertently to pronounce what we hear. The more different sounds you hear, the more easy it becomes to learn foreign languages with little accent later. As far as I know, German is neither extremely limited in sounds, nor excessively complicated.
   Germans have distinct difficulties in certain foreign languages, because German doesn't contain that sound. The most famous example I can think of is the "th" sound in English. Germans will pronounce it "s" instead.
   That is similar to Chinese who struggle with all kinds of "r", replace it by "l", and thus a Ferrari becomes pronounced Fallali.
   
   French contains the nasal sounds for vowels which are really tough for most foreigners including Germans.
   
   Spanish has the rolled "r", which is even much worse for Chinese, and many Germans can's say it either.
   
   All of this shows, reversely, that German has no extremely complete set of sounds, and thus can not be so difficult in that respect. (Grammar is a very different matter, I have written several times about that on Zhihu)
   
   From what I heard, Russian is one of the most complete languages in that respect, making it relatively easy for Russians to learn foreign languages.
   I speak a little Polish, which is quite similar to Russian, and I can say that for Polish, I need basically all sounds combined that I learned on top of German in Spanish, French and English. It's a nightmare.
   
2. But I think the second point is even more important: In total contrast to French, and to a lesser extend English, German has very precise equivalents between the written and the spoken word. If you know how to say our alphabet, and can read the letters, you can almost read.
   
   I am just experiencing that with my older son (6) again. He can read now, and is also writing a little.
   In French, the spelling is a nightmare, because 1 pronunciation can have many different written equivalents.
   
   E.g. the letter "o" sounds exactly like the word for water "eau" (singular), or water in plural "eaux".
   How is the poor child supposed to know that? I could write a book full of similar examples.
   My wife's one grandmother actually came from Hungary. She lived in France for half a century, but never learned to spell correctly.

Now to Carlos I

I suppose you refer to Charles V (Spanish: Carlos; German: Karl; Italian: Carlo; Latin: Carolus; Dutch: Karel, born 24 February 1500 – died 21 September 1558) was ruler of both the Spanish Empire as Charles I from 1516 and the Holy Roman Empire as Charles V from 1519, as well as of the lands of the former Duchy of Burgundy (French!) from 1506.

People say that in his empire, the sun never set, because he had the Spanish America in the West, and even colonies in Asia, and finally split his kingdom because he felt it was too big.

So he is well places to speak all those languages.

So first of all, he wanted to say: "I need all those languages, because my kingdom spans all those different populations. "

Secondly, he wanted to say: "Different languages have different strengths and weaknesses.

• Spain at the time was the center of gravity for the Catholic faith, so that was for god.
• Italian is considered by many to be the most beautiful language. That has to do with the fact that it consists of the highest proportion of vowels. So Italian is great for romance (French is similar in those respects, it's a question of taste, some prefer French, some Italian).
• "Chilling with gentlemen" is also very social, so why not in French?
• German however has the reputation among many people to be an "ugly" language. Not difficult, but simply not sounding nice. That might have to do with certain sounds in the throat, and certainly with the relative lack of vowels and probably also intonation: French and Italian have a "melody", almost like a song. German doesn't.
  But again: That means, YOU don't have to learn it either.
  
  In fact, many French will say that German (and even more Dutch) are like if a dog barks. That might be harsh, but I gladly admit that French is much more beautiful.
  
  In fact, the Germans themselves are totally in love with the French accent. It makes the speaker instantly very charming.