Bobbyzan:
The plan is to send it attached by a friend’s truck registred in Eastern Europe wich will be here in Uk to tow it. I don’t know if I can make here the provisional plates for the trailer only to transit up to Bulgaria.
You cannot make any export or provisional, registration plates in the UK, because the UK does not issue any registration documents, numbers, or plates, for trailers. UK law only requires motor vehicles to be registered, not trailers.
When a UK trailer leaves the UK it will be perfectly legal without its own plates, but should display the number of the vehicle towing it. If the trailer is owned by a BG person or company, then it should follow the laws of BG shouldnt it? So, any registration laws, documents, and plates should follow BG laws.