So for me, as I stumble and bumble my way through learning French (mostly through DuoLingo, hey), I'm often thinking about this issue.
Now-- on the surface of things, Modern English is almost exclusively comprised of German & French, and almost every word in these sentences are specific examples of such in terms of direct etymology. Which is a big part of why I've typically regarded French & German as my sibling languages. It's a nice, bright thought, anyway!
Let's take the modern English word "fight"-- WP claims:
From Middle English fighten, from Old English feohtan (“to fight, combat, strive”), from Proto-West Germanic *fehtan, from Proto-Germanic *fehtaną (“to comb, tease, shear, struggle with”), from Proto-Indo-European *peḱ- (“to comb, shear”).
My point is that there's so many ways to run with that over time... in any language whatsoever! Indeed, IIRC there was a "fisten" variation which meant an entirely different thing in earlier German.
But, "shear?" Yes, yes back in my schoolyard days, I wanted to shear my opponent like a little lost lamb, but... I don't think that's right.
So here's my point, assuming you've lasted this far. Modern German in fact split from modern English maybe around ~~800AD? And Modern French, around... perhaps slightly earlier than the Norman Conquest (1066), meaning that even though Modern English is absolutely PACKED full of French & German pronyms, we can't just assume they mean the same thing, anymore, as with the examples above.
It sort of breaks my heart, but it's just reality, non?
Language has always changed and evolved. It feels sad to lose something but other than documenting a "dead language" or dialect, not sure anything else can be done. You can force yourself to learn it if it is close to your language but then you also have to use it, or it will vanish again.
I remember reading about this Welsh PhD or Master student, I think it was for Chemistry. They were the first student ever to do the whole studying completely in Welsh. Including the thesis. They had to invent new words for scientific terms since they didn't exist, I think they worked together with some association for Welsh language or something. But all of that will be gone if no one else is picking it up and in the sense of science it is also not a great decision because now you limit who can understand your work to the Welsh speaking community. Since you invented new words, maybe even those won't get what you wrote.
My point of rambling, I am not sure you can do anything about changing languages. They are meant to be used or not. So while it feels like a sad thing to lose some languages, it should not because its just how languages work. Not sure that makes sense to say...
Absolutely, I totally agree. It's Impossible to artificially keep a language alive, and forcing people to learn/use a language is wrong.
It's just sad, that's all. It's like seeing a local shop close and getting replaced by a shopping mall, and then that mall closes and is replaced by internet shopping. Reality moves forward, but it's not necessarily a bad thing.