If you could add custom templates, you could let the community add the country specific things

I'm leaving this link here regarding the "EU e-invoicing standard CEN 16931"

https://ec.europa.eu/digital-building-blocks/sites/display/D...

I don't know how complicated or easy it would be to just create templates which satisfy this.

In Germany it's already required for B2B transactions [0]

  In principle, the following formats will comply with CEN 16931:
  ZUGFeRD: Hybrid format: Human-readable PDF/A-3 with an embedded XML file in the syntax "Cross-Industry Invoice" (CII)
  XRechnung: XML file in the syntax "Cross-Industry Invoice" (CII)
  XRechnung: XML file in the "Universal Business Language" (UBL) syntax