The website also has info pages about the authors: 3 from Spain and 1 from Andorra.
The first language of all authors seems to be either Spanish or Catalan.
Also it is common to stick to the comma as decimal separator and dot as thousands separator when writing English. This convention is independent of the language used.
Same goes for date notation, dd-mm-yyyy is used (almost) always.
In Windows or Linux for example you can select the English language with Dutch localisation. It's used by almost all software developers I know.