[Feature request] support for german keyboard

[nkappler]

Hi,

First of all, thanks for this awesome tool, I must have used it a thousand times ❤️

In case you don't know, in Germany period and comma are basically swapped in the number system.
so one million would look like this:

EN	DE
1,000,000.00	1.000.000,00

As a consequence, on the numberpad of german keyboards, there's a comma key and not a period key.
This means that if you want to enter float values (eg. 0,5 [ie. 0.5] ) in a number field in the calculator,
the calculation breaks because 0,5 is not parsed as a valid number.

My suggestion is to handle comma keypresses as period keypresses 😊