I agree that, when speaking to one's "good friend," logic would suggest that "ty" would be more appropriate than "vy." But for purposes of learning words and how they fit together grammatically, I can see why "vy" is accepted. Whether "ty" would be rejected in, say, a Write This in Czech exercise, I don't know... if there is such an exercise, I may try it!
thanks. interesting. Google Translate gives 'dude' as a translation which is very matey/informal used mostly by young adult/teenage Americans. I thought it was quite 'cute' and intimate when I heard it! It seems from your link that it could also be like 'comrade' which I could imagine giving offence almost in a Czech cultural context.
It can be either disrespectful or not, and most of the time not a putdown to be called dude. However, a dude originally was a newby, someone on the ranch who didn't know anything about riding a horse, working a ranch, being around a farm and its animals. A city slicker. Therefore, the term "dude ranch" came into being where anybody could go "live" on a ranch for a week's vacation. So that's some background on the negative connotations that may be implied at times. I am very familiar with this term and it's still used in Texas to apply negatively at times, but it's not particularly harsh.
Because Žofie is declined the same way as růže or ovce. Those also have vocative the same as nominative. You have to learn which paradigm belongs to which name like in any other noun you learn. Often you can guess from the ending. There is only one feminine paradigm ending with -e.
No. Přítelkyně can be just a good friend. Though typically you speak about two women being přítelkyně of each other in non romantic manner. When you say "jeho přítelkyně" she is a girlfriend. Přítel - přítelkyně are little more than just friends. They are good, intimate friends. At the same time the word in that meaning is slowly becoming archaic. In girlfriend meaning it is still used.
Originally, the meaning of "přítel" and "přítelkyně" was just a friend - it is still being used in that way in more formal speeches or literature. In today's informal spoken language, however, it is used almost exclusively to refer to a romantic relationship. The common way of referring to friends is saying "kamarád" and "kamarádka" - there is no ambiguity there, no romance whatsoever, but its less formal.