Hi! Not sure if my memory is failing me... But unless it's different to how we applied (and pretty much continue to apply*) EU law in the UK, you can have a name on front of pack but then there is a "legal name" requirement. That's normally on back of pack above the ingredients listing or nutritional. Unless there is a specific bit of legislation or it's a really well known and understood simple foodstuff, you'd make that a descriptive name.
So for example, on this product which is also a gyoza on a UK website, you can see the legal name on the online information:
https://www.tesco.co...ducts/299955276
The legal name they've put here is a description, i.e.:
"Steamed Asian style wheat parcels filled with chicken & vegetables"
And on front of pack they've called them "chicken gyoza".
I wouldn't personally call them "Japanese gyoza" unless they're actually made in Japan. It was drummed into me in my legal labelling course that one of the most fundamental principles is "you should not mislead the consumer".
Hope that helps but even within the EU there can be the odd nuance.
(Also *wasn't that a bloody waste of time and no, there was no way I voted to leave. I voted to stay along with the vast majority of the food industry.)