I think "sorry" is only a rough equivalent for the shorter version, "извини"
I am not sure why you got downvoted.
You are correct in the sense that извини is the informal version.
Duo's take in this example seems to be that English sorry is more informal than excuse me. The Russian usage in the example is formal.
I agree with them in the sense that I personally consider excuse me to be a bit more formal. I would use sorry in this particular sentence because of that. I would only use this particular sentence in a situation where I already was in conversation with someone. Under those circumstances I personally use informal and be damned if someone not participating in the conversation doesn't like it.
If I was interrupting someone I would use the more formal excuse me. If I approached someone and said I don't understand that sign I would use the more formal version both in Russian and English.
But that is just me. I consider excuse me to be more formal than sorry. The Russian example uses the formal version for whatever reason and want what I personally regard as the more formal English version.
Maybe Duo is just chastising me for my personal excessive informality in Russian and English and have no other point to make. Or they maybe they just fell asleep on this example, screwed up big time and simply forgot to include sorry in the range of acceptable answers.
But Russian formal should actually result in English formal in translation if such exists. Does it exist? I believe it does but I did get it wrong when I first hit the example. But getting it wrong made me think about the whole informal/formal thing. Maybe, just maybe, that was Duo's point.
I invite haters to downvote my comment as well. I mean ...why not, if it makes you feel good.....
Yes, I wondered if he meant that извини is a rough equivalent of извините because it is informal and is more like sorry instead of excuse me in English. He could just as easily have meant that the short version means more than sorry/excuse me to the point that the short and long versions of the word were only loosely connected in Russian.
Most of my comments are about the English involved rather than the target language but because I don't know for sure what the usage is in that language. Naturally many people have their own take on the English part and are quick to point it out to me. Whatever the intention of o.p. I agree with Duo on their apparent understanding of the English use of sorry/excuse me which they seem to say is the same in Russian.
My response was mostly intended for the benefit of the several posters who started new threads on this comments page that were simply repeats of each other on the this same topic.
Downvoting is something I do when the comments are not just obviously wrong but contain openly expressed ridicule for those who are actually correct. I am much more free with upvotes of course.
Ah, I see. My apologies.
In that case, try to set up a 'keyboard-swaping' shortcut. I have mine set up that pressing "Windows-Flag + Spacebar" switches me between English and Russian.
I am using Ubuntu, so I could help you with that one, but I don't know about other operating systems.
Ah, ok. Well, assuming that you have a GUI (and not simply a terminal), if you go to "System Settings -> Text Entry" there is a "+" arrow to add additional languages, so I added "Russian (phonetic)". Then go to "System Settings -> Keyboard -> Shourcuts (tab) -> Typing (left-hand list)" and you can choose what to type for "Switch To Next Source", and then there you go!
Your answer isn't a translation of the Russian sentence. It may mean the same thing in limited circumstances. Without context, it usually means something else entirely.
It is easy to imagine a context where you say you don't understand Russian. Listeners will immediately assume that that they know what you mean.
It is harder to imagine a context where you say you don't follow Russian. Your listener will have to guess at what you mean by saying you don't follow it.
If you said to me you don't understand Shakespeare I would think that it has something to do with the English used or the deeper meaning attributed to his writing.
If you said you don't follow Shakespeare I would assume you were making the point that you were not a Shakespeare groupie hanging out on Google Shakespeare groups, going to Shakespeare festivals in costume etc.
The example says someone doesn't understand. He may well be saying he understand anything at all about anything.
Your translation says that there is some specific thing that he doesn't understand and the speaker believes it is clear to the listener what it is that he is talking about.
The choice between "Izvinite", "Prostite" and informal versions depends on age of the person you converse. Russians use these words to apologize for disturbing a person or interrupting something or somebody. I would translate the sentence as "Sorry, I don't understand." if the person feels apologetic. Humorous "Ya diko izvinyayus'" can add another gradation.