In that case, the dot should be present on the keyboard as well, instead of the comma. In that case it would indeed be consistent.
The most consistent would be, if the Homey app would reflect the language/display settings on the mobile phone.
As far as my knowledge goes, the numeric keyboard could be displayed with a minus sign also visible.
I think I cannot change the keyboard, its the responsibility of the app maker to show me the numeric one, the alfabet one, an email variation to that, etc.