So you're arguing about a name for something they offered as a stopgap as they were not willing at that time to call it by the other name due to others not wanting us to have marriage. Even in other countries that introduced it it was a way of bringing in same sex unions even if offered to opposite sex couples as a by-effect
If you feel strongly about it the please campaign for it, I won't argue against your rights to a legal marriage...woops civil partnership .
As for international limitations its not up to the UK but for everyone else to recognise it. That's a lot of rules in a lot of other countries that need changing.