Document generated in Journey task always generated with en_US locale? How to fix?

Summary:

We're generating a PDF in a Journey. The issue is with number formatting.
The format of the field us set to Number with mask "#.##0,00" because we need the Dutch number format (it is showing a salary, which should use the comma as the decimal seperator).
When editting and running the document in Word (through the BI Publisher plug-in) everything is fine.
As soon as the template is used to generate the document, the US formatting is applied.
It does not matter if the document is generated in OTBI or from the Journey task that triggers it.
The RTF template is uploaded with Dutch (Netherlands) as the locale.