Two very different kinds of paper
A marriage record and its translation sit together in the same folder and look much alike, yet they behave in opposite ways. One is entered in a register that keeps it indefinitely and can print it again on request. The other exists only as the set in your hands. Knowing which is which changes how carefully you look after each.
The record side of it
Stoke-on-Trent Register Office holds certified copies of civil records, marriages among them, at the Civic Centre on Glebe Street, and it works by post rather than over a counter. A certified translation of a Marriage Certificate in the United Kingdom starts from one of those copies. If the copy is lost, torn or stained, another one can simply be ordered.
The translation side of it
Nothing equivalent exists for the translated pages. No public office keeps them, indexes them or reissues them, because no public office made them. They came from a named translator who wrote them and put a signature to them. Losing that set means paying for the work over again, which is a small cost handled carelessly and an avoidable one handled well.
Who signs, and what is attached
The signer is an ITI or CIOL-qualified certified translator, and the form used is the kind UK authorities such as UKVI and GRO accept: a dated statement of accuracy fastened to the pages it covers. Nothing at all is added to your marriage record. The original sheet is not marked, stamped or altered by any part of the work.
Cost, days, and keeping your set
The rate is £25 for each side of paper as the record was issued, with 2–3 business days as standard and 24 hours on the express route. When the set arrives, put it somewhere you will find it again and scan it before it goes anywhere. That habit costs you nothing and saves the whole job if a folder ever goes astray.