It's well and widely known that languages evolve over time. Sometimes they change if words fall into disuse ('haberdasher' in English), a word takes on a new meaning (historically, the Arabic word for 'house' meant 'tent'), proximity to another culture (the British Isles being repeatedly overrun helped produce English as we know it today) or sometimes for no clear reason at all (the so-called Great Vowel Shift responsible for the English 'burning' versus the German 'brennend').
Periodically though, pronunciations will change simply because they're easier to say. Euphonic assimilation is responsible for 'goodog' as opposed to 'good dog' in English, but sometimes the change will actually alter a letter. Eventually it may be accepted as the common spelling. Typically though it seems to be confined to 'classes' of letters. A 't' may evolve into a 'd' for example, as they are both 'dental' letters, produced through a similar process involving the speech organs.
While listening to the song 'Vergissmeinnicht' by Eisbrecher recently, it dawned on me that 'vergissmeinnicht' meant 'forget-me-not' ('eisbrecher' incidentally, means 'ice breaker'). It's a fairly obvious conclusion even if one (such as myself) doesn't speak German.
F and V are both labiodental fricative (I've also seen them referred to as 'plosive') letters. The difference between the two of them being that V is voiced and F is not. It's easy to see how over time one letter could gradually be replaced by the other. The major limiting factor as I see it in English is that there are English words that already are 'place holders', prohibiting some changes from taking place. 'Very' would have a hard time becoming 'fery' as 'fairy' and 'ferry' already exist. Not that it's impossible, but it would seem to me to be easier to transition if there were no sound collection already existing.
Language is a very time-sensitive subject. Some researchers think that spoken language evolved out of a need to warn others in the pack about impending dangers. Clearly there's an advantage to being able to warn others quickly. As such, it makes sense that spoken language would, like electrons in an atom, seek a 'low-energy' state where the least amount of energy was exerted to communicate the message.
This implies perhaps that some transliterations are more likely to happen than others. A Z is more likely to evolve into an S than vice versa as an S is easier to say. Hence the name 'euphonic'.
Anyway, it seems that an F is a more 'natural' letter than a V as a voiced letter should always require more effort than it's unvoiced alternative. Since the English equivalent of vergissmeinnicht starts with an F, it seems to suggest that perhaps the original shared root started with an F which was the sounds maintained by English. The questions then arises as to why a language would intentionally adopt a sound that requires more effort? The alternative is that the original root contained a V sound and while English has settled on an F German maintains the original sound.
The second syllable consonant, G, is shared by both languages.
The puzzle for me is the third syllable. English uses a palatal T sound whereas German has an unvoiced sibilant (or palatoalveolar fricative). The sister letter of T is D and that of S, Z. Were German to use a D here or English a Z the resemblance would be clear but I'm at a loss to explain why we're left with the two sounds we have. It's possible I suppose that S evolved out of a now lost palatal sound similar to an open 'sh' sound.
Looking at the two sounds we have to work with, the S seems to me to be the winner in terms of ease of pronunciation. Could it be that in the ages before Germanic split into upper and lower Germanic the root was *FGS (for those of you playing along at home, the * indicates a supposition or uncertainty)? I'd love to know. If an email was sent out detailing this at some point, I didn't get it so please forward it to me.
As for the rest of the word, 'mein' is a fairly commonly known German word, as is 'nicht'. Being the semi-agglutinative language German is, they all get slammed together. I guess we English speakers prefer hyphens.
Since I spent so much time on it, here's a chunk of the song that spawned this whole diatribe:
Verzeih mir - bleib bei mir
und ich sagte noch Vergissmeinnicht
Ich schenk dir zum Abschied
ein letztes Licht
Forgive me - stay with me
and I still said forget-me-not
I'll give you as a goodbye
one last light