Both the German and French languages, along with English, evolved from the same roots. This is reflected in some of their words and grammatical structures. So then why are the pronunciations of both languages so different? Why is German so harsh with more emphasis on rough sounding letter combinations (st, sh, tz, ch) as compared to French (which I know is a Romance Language but have no clue as to what it means)?
That French is a Romance language means it is descended from Vulgar Latin (the spoken version of Latin, as written Latin was more conservative). English and German aren't descended from Latin (they are Germanic), although they have many words that ultimately come from Latin (especially English), but that's a very different concept: those words were borrowed, usually from French, at some specific point, and became loanwords; they didn't just evolve from words that already existed in the language.– LjLNov 8, 2018 at 19:07
The short answer is, sounds change really fast. Compare different regional accents in English (Southern, East Coast, Australian, Indian)—outside of Britain, all of these differences have arisen in the past two hundred years or so. Or look at some of Shakespeare's rhymes, like "love" and "prove", or "wind" and "kind", which rhymed perfectly in his day.
The long answer is, it's been a long time since the family tree of French and German split apart. By most estimates, their last common ancestor (Proto-Indo-European) broke apart over five thousand years ago. One branch became Germanic which eventually evolved into German (and Dutch and Icelandic and English and…), while another became Italic, evolving into Latin, then French (and Spanish and Romanian and Italian and…).
Now, French and German are spoken in close proximity, and so they're having an effect on each other—but they've been close for a relatively small amount of time. It's entirely plausible that in time Standard German will gain nasal vowels and Standard French affricates, but at present that hasn't happened.
As a side note, the "harshness" or "roughness" of a language is very difficult to measure. You say the "sh" sound is harsh, but what makes German Schiff "ship" any harsher than French chat "cat"? They start with the same sound. A lot of it comes down to individual perceptions rather than anything quantifiable.
A quibble: Standard German does have nasal(ized) vowels in French loanwords like "Teint".– fdbAug 8, 2019 at 11:23
@fdb Huh, are those actually phonemic nasal vowels? I would have pronounced it something like
/tajnt/, with the vowel being allophonically nasalized before a nasal consonant.– Draconis ♦Aug 8, 2019 at 12:51
1Click on "Aussprache": dwds.de/wb/Teint– fdbAug 8, 2019 at 12:57