The bbc article claims in the UK (and “many countries in Europe”) start with the thumb, but the Inglorious Basterds scene seems to contradict that.
The business insider article also claims people start counting with their thumb in Portugal but I start with the index finger and while I’m not sure everyone else does it, I think using the 3 middle fingers to represent the number 3 (like the British spy) is far more common than using the thumb.