hang on there, people.
German has an unvoiced "w" sound like in "Wald", which sounds different to the English "wood". The English sound requires much more rounding and tension of the lips when producing the "w".
Since Germans don't normally round the lips when uttering the "w" in "Wald", they also don't tend to make the effort when pronouncing similar looking words in English. Hence, when a German native speaker says "wood", to most English ears it will not sound "pointed" enough and the "w" sound is interpreted to lean towards v rather than w.
German also has an unvoiced "f" sound like in "fallen", which sound the same as the English "falling". These sounds are mostly unproblematic for German learners of English.
English, however also has the voiced "f" sound, like "very", "volume", "variety"
This sound is what Germans struggle with most, since that voiced "f" does not exist in the native German sound scheme.
Add to that the confusion of which consonant is actually pronounced in which way and you have pinned one of the major dilemmas of German accents. In German, there is "Vater" with an "f" sound and "Vase" with a "w" sound (although in my regional dialect, we'd always use a voiced "f" instead of a "w" for Vase, but that cannot be applied to all of Germany),
So, whenever a German speaker comes across an English word with a v, they have to decide whether or not to apply the German "f" like "Vater", or the "w" like "Vase" or the uncomfortable voiced "v" like in "very", which their speech apparatus may note even be able to produce correctly.
(Remember that the formation of sound patterns are pretty much internalised within the first 10 years of life and after that most people are physically not able to learn to produce different sounds with their speech apparatus. It's the gift of children to learn more than one language without any conceivable accent. Once you've topped the age of ten or twelve, you'll probably have an accent for the rest of your life. I can find sources for that if required).
For Germans, it's already difficult enough to pronounce the English "w" sound with pointed lips and remember to get it right each time: What, Where, When, were we walking or why not? This is quite an exercise for a German native.
"F" is easy. Been there, done that. Feel it. "Fühl mal." No prob.
But the voiced "f" in "very varying varieties of vases" is about as much as you can challenge a German speaker. "Vase" is the same word in German and pronounced "wase" in most German regions. The other v sounds are not native German sounds, so a substitute must be found. The first, unconscious impulse will be to substitute them with a more familiar sound. And since "vase" is clearly a German "w", there's no surprise that the v sounds will be pretty close to the German variety of "w" when that sentence is pronounced by a German speaker.
Hence: "*Wirtual reality"
This is an unconscious process. It can be influenced by training. People who actually LISTEN to their own pronunciation will notice a difference to native speakers and may choose to correct their pronunciation. In most situations, though, non-native speakers have stopped to LISTEN to their own pronunciation. Add to that the physical inability to learn to produce new sounds after your speech producing muscles have honed in at a status quo when you're abpout 10 years old, and there's your foreign language accent.
Henry Kissinger was 15 when he moved to the US (if I remember correctly). He had a German accent throughout his adult life. His younger siblings were much more successful in adopting to the language of their new country of residence and did not have an accent, at least not as strong as Henry's.