Something changes once a language is standardized, and that standardizationis malleable in direct relation to how important the "standardized language" is to the current culture.

Like Vampire said, Standard Arabic is very conservative because the Quran is considered holy only in the form of standardized Quranic arabic. So, you can see Modern Standard Arabic as being a ship with an anchor in the Quranic language and thus moving very little.

Regarding many European Languages, there was a standardization around the time of the protestant reformation because of the translating of the bible into languages. The example I'm most familiar with is the Dutch/German separation based on 2 major translations done in the area near Amsterdam and in the highlands of the German south. Translators were the closest thing to modern linguists, and attempted to find the most broadly understandable way to write something (with, of course, class differences and such taken into account). And people became grouped geographically by which translation they could understand well enough. To extend the anchor metaphor, this bible translation was similar to the Quran but without the specific necessity for not changing. So it had a braking effect with regards to diverging linguistic trends, but can't really be called an anchor.

I'm sure some people understood that this was an interesting development, where they were not only expected to do simple trading/travel across a Sprachbund, but were expected to understand writing and complex concepts in a specific wording. The consequences of that might not have been fully realized. That is a super interesting thing that I want to study a bit into.

English had Shakespeare as possibly the biggest braking trend in the past 300 years (up until WW2). I find it really interesting to try to analyze how much English has changed after becoming the Lingua Franca of most of the world relative to before that. Does being spoken broadly cause converging or diverging change? I assume is has a strong converging element, but does that converged lanuage also change faster (think of spreading of memes)?

idk if i gave any answers, but I also love thinking about this

Conservative is the word you're looking for.

Icelandic is very conservative. Standard Arabic is kept conservative partly by the Quran.

One way to measure the speed of change is with a Swadesh list.

The fewer speakers a language has, the faster it's likely to evolve. More widespread languages can undergo pronunciation changes, but the core vocabulary stays pretty fixed.

The colonial nature of England, France, etc. is exactly why these languages have a reputation for adapting and evolving.

France may have fought it extremely hard with their institutions, but even they can't stop the African continent (that largely sees "pure" french as a colonial relic) from adapting french to their cultures to the point that Africa is the driving force of French now.

Languages evolve much like animals do I guess? The same way isolated communities can diverge, or how language dialects can rapidly change when material conditions change. when you have such a massive international community of speakers in your language, there are many more opportunities for material conditions and isolation to drive linguistic change. And now, thanks to the internet and mass media, these changes can be shared across the language instead of diverging beyond intelligibility.

Thoust must Returneth to ye olde English