How can i get a double from string with starting 0,

the comma lets interpretate the Conversion function in default mode that it is a GroupSeperator and is not recognizing the comma as decimal seperator.

we can do it eg like
grafik

First line is parsing 0,70 by applying local numberformats into a double correctly
We do see it as 0.70 is the internal representation of this number
Kindly note: the internal format of Double we do not touch. In case of we do need another format representation we do it by toString (line2)

So just adopt the locals to your country: e.g. tr-TR for Turkey
grafik