That is true, Yiddish was always influenced by the country they are spoken in, for example in Israel they use a lot of Hebrew words instead in Hungary back in the days they used to use Hungarian words etc.
Though I do think over here we have way more English words mixed into Yiddish then in other countries.
Of course. American Yiddish is very different than Israeli Yiddish - but I think everyone can understand each other pretty well by using context.
I was in Estonia a few weeks ago and trying to have a conversation with a bunch of locals at the Shabbos meal. Their English was terrible and my Estonian and Russian non-existent. We weren't communicating very well until I thought to try in Yiddish - and then we sat and schmoozed for
hours. I didn't understand every single word they said and I'm sure it went the other way as well, but the language was the same and we got along swimmingly.
Now if you'd put me into a room with the Harry Potter dude, we may as well be speaking Mandarin.
That's the real difference between Chassidish/Chabad/Israeli/European/whatever and what I call YIVO Yiddishist.