Well it depends the scale we're talking about. If it's just the vocabulary then yes people gain and lose words and grammar bits all the time. Preussisch for example had lots of words with Lithuanian influence (including a different word for bier!!) that I could see Prussia dropping as soon as he permanently relocated to Berlin. And at least with learning Hochdeutsch the Germans are probably all bidialectal at the least.
But phonology is a lot harder. Like take for example a change that happening in the US at the moment, we call it the caught-cot merger. Are the words caught and cot pronounced the same for you? For me they're not, and for most people in NY/NJ and northern PA they're not. But for most Americans, at an increasing rate they are (I was always a guinea pig to explain this at Uni because I went to school in Mass lol). But the thing is I've lived in places with the merger more than without, I have full academic knowledge of it, and of the fact all Americans will probably have it eventually the way dialect change is going, and yet I can't pronounce them the same if I tried. They're just naturally different.
Now that is just one little change to one little word, but consider at the time of the American Revolution America and England would have sounded exactly the same. And in 2014 America likely speaks General American English and for simplicities sake we'll say England uses Received Pronunciation. That's a lot of changes going on, I mean RP English has ~7 more vowel sounds than we do!!
Codeswitching will almost assuredly occur to a degree but it's a matter of when. Neither of us speak General American English but America wouldn't need to codeswitch for us, but if he still sounded like he did at the Revolution he would have to to not sound 'foreign' and it's worse with England, after all Shakespeare is Modern English, the transition from that to what we speak today was slow but with nations' fucked up sense of time it could have been in the blink of an eye for them.
And the thing is, even if you take the approach that they just adopt every sound/vocab/grammar change they come across (ludicrous!!) and they're polydialectal, all languages even your native one need use to maintain, so it's very possible they can't understand their past selves at all!! (sidenote: Germany could, he's too young. But Teuton and HRE are likely incomprehensible) And oh god, Germania probably sounds like a mix of all of their dialects plus weird sounds and words they think they've heard before but don't understand of jesus he might as well be speaking chinese!
Re: ooc
But phonology is a lot harder. Like take for example a change that happening in the US at the moment, we call it the caught-cot merger. Are the words caught and cot pronounced the same for you? For me they're not, and for most people in NY/NJ and northern PA they're not. But for most Americans, at an increasing rate they are (I was always a guinea pig to explain this at Uni because I went to school in Mass lol). But the thing is I've lived in places with the merger more than without, I have full academic knowledge of it, and of the fact all Americans will probably have it eventually the way dialect change is going, and yet I can't pronounce them the same if I tried. They're just naturally different.
Now that is just one little change to one little word, but consider at the time of the American Revolution America and England would have sounded exactly the same. And in 2014 America likely speaks General American English and for simplicities sake we'll say England uses Received Pronunciation. That's a lot of changes going on, I mean RP English has ~7 more vowel sounds than we do!!
Codeswitching will almost assuredly occur to a degree but it's a matter of when. Neither of us speak General American English but America wouldn't need to codeswitch for us, but if he still sounded like he did at the Revolution he would have to to not sound 'foreign' and it's worse with England, after all Shakespeare is Modern English, the transition from that to what we speak today was slow but with nations' fucked up sense of time it could have been in the blink of an eye for them.
And the thing is, even if you take the approach that they just adopt every sound/vocab/grammar change they come across (ludicrous!!) and they're polydialectal, all languages even your native one need use to maintain, so it's very possible they can't understand their past selves at all!! (sidenote: Germany could, he's too young. But Teuton and HRE are likely incomprehensible) And oh god, Germania probably sounds like a mix of all of their dialects plus weird sounds and words they think they've heard before but don't understand of jesus he might as well be speaking chinese!