As with MicroStation, the OpenCities Map Label Coordinates tool does not respect the Windows Operating System Regional settings with respect to numeric formatting.
Bug 657896 has been filed to address this issue. 

Users seeking application of the 'decimal comma' format for the coordinate labelling tools are thus limited and must seek alternatives. 

Demonstration:
Here we demonstrate the nominal Label Coordinates behavior (formatting insufficient for decimal comma) and the allowances (Units Separator, Use Comma for Decimal) available via Dimension Style formatting to achieve decimal comma format for dimensions.  Key-in commands and the (F4) Ribbon Search tool are utilized for simplified replication. 
* OpenCities Map PowerView users should note use of DIALOG TOOLBOX XYZTXT and LABEL POINT commands, as the ribbon hosting Label Coordinates is not available within the Map PowerView interface. 

Workaround: 
Here we demonstrate creation of a cell utilizing a Placeholder Cell Properties type Text Field to achieve functionality similar to that of the Label Coordinates tool.
'decimal comma' formatting is achieved through formatting options (Decimal Separator, Thousands Separator) specific to the Text Field.   As Text Field use involves de-facto display of the  Text Field background, we conclude with demonstration of some options applicable to Field display modification. 

* An alternative to Placeholder use, could be Element Properties Field Type applied to another element expected to exist within the resulting cell. (e.g. Center property of a Circle element).  Also shown: Prefix and Suffix can be applied wholly within the Text Field if desired to streamline the element formatting, e.g. to allow for use of contrasting field background border.