Adding English names to the name:cy tag does seem to be corrupting that tag. In openstreetmap if an object has a single name then it belongs in the name tag.

Likewise for Tesco and Burger King. So not sure what you are trying to achieve with these edits, they seem to be diminishing Welsh names rather than enhancing them.

Now if there was a law to rebrand Burger King as Burger y Brennin then I would be all for it.

Diolch Phil