Proper pronunciation is interesting. Even within American speaking America the pronunciation of words varies based on region or state or general geography.

Principal Skinner: Yes, it's a regional dialect
Chalmers: uh huh. what region?
Skinner: upstate new york
Chalmers: Really. Well, I'm from Utica and I never heard anyone the phrase, "steamed hams."
Skinner: Oh, not in Utica, no; it's an Albany expression.

[though tbh they were talking about slang not pronunciation]

Also pronunciation can be varied based on genetics. For example Asians tend to find certain sounds difficult to produce, and so their language is shaped around the sound[s] that are more...intuitive, for a lack of word. Obviously I am not saying they CANNOT make the sound, but you can even see it with me when I try to say [for example] 'their'.