Not a big problem in everyday life, it took him over a year to realize that she counted differently than him when using her fingers.
The difference isn't too big but it is noticeable.
In Germany, counting begins with the thumb. (She wants to point out here that she thinks that making one with the index finger is also popular these days).
Two is made by using the thumb and index finger.
Add on the middle finger to make three.
Four and five are the same as in the USA. Keeping only the pinky down to make four would be next to impossible for most people we guess.
Counting in the USA begins with the index finger and the thumb is not used until making the number five.
A little lesson for the next time you are traveling and want to order a beer.