I've also heard that one of the biggest 'tells' of (American?) English is how the 'r' is pronounced with the tongue unnaturally forced into the back of the throat, so when movies try to create invented languages, they tend to avoid that sound, and it makes it sound more foreign or alien. It's also one of the harder sounds for children to learn.
https://www.youtube.com/watch?v=A_a256A5RFQ
This is an unknown Indian language:
https://www.youtube.com/watch?v=i3wTY00564Y
https://www.youtube.com/watch?v=Zz9pXe4PbRQ
Dutch:
https://www.youtube.com/watch?v=ucB84k0G3EU
Korean, at least mostly:
https://www.youtube.com/watch?v=S5ZfW1XzAgA
https://www.youtube.com/watch?v=nvASlcUuCZI
https://www.youtube.com/watch?v=QN_E6HCuE5A
https://www.youtube.com/watch?v=oHf1bKw_ftI
Possibly Chinese:
https://www.youtube.com/watch?v=DK2gdO31pYs
Japanese:
https://www.youtube.com/watch?v=EwrqzGBNvGY
https://www.youtube.com/watch?v=dt6RuccJdAo
https://www.youtube.com/watch?v=TcdYbEangV4
Seems like a Germanic or Slavic language:
Warning: Kay has a strong Northern English accent and heavily uses local idioms so I hope the humor isn't lost on an international audience.
And I wont mention the accents in peaky blinders :-)
In Dutch the phenomenon is known nowadays as a "Mamma Appelsapje" (a "Mommy Apple Juice"), because the Michael Jackson song "Wanna be starting something" contains
> mama say mama sa mama coosa
Which sounds to Dutch speakers like
> mama say mama sa mamma appelsap
Another one is Chumbawamba - Tubthumping, where
> You're never gonna keep me down
Sounds like
> Jullie hebben nog niet betaald
Which means "You haven't paid yet"