The translator signs first
Every certified translation of a Translator's Affidavit in Belfast rests on one name: the translator's. The declaration is written in the first person. It says that the person who produced the new text stands behind it word for word. It gives their credential, the date and both languages, and it is bound to the pages it describes so the two cannot drift apart.
Who watches the signing
Then the signature is witnessed. This paper is a private act, not an entry in a public register. A solicitor or a notary public must see it signed before an authority will accept it. In Belfast that witness works inside Northern Ireland's own legal system, which sits apart from the one in England and Wales. The signed page still reads the same either way.
What the seal really says
A seal covers less ground than most people expect. The solicitor or notary is not reading the target language and is not marking the work. They attest to identity and to the act itself: this named person, seen in front of them, wrote this signature on this date. Accuracy stays with the translator. The seal is what turns that word into an official translation of a Translator's Affidavit in Belfast.
The same rule, wherever the witness sits
The city boundary changes nothing here. A certified translation of a Translator's Affidavit in United Kingdom practice rests on the translator's signed statement of accuracy. A solicitor or notary witnesses that signature, wherever either of them happens to work. UKVI and the General Register Office read a Belfast bundle exactly as they read one from anywhere else.
Start from a clean source paper
Where the statement sits on top of a civil record, get a fresh certified copy before any of this begins. The General Register Office for Northern Ireland (GRONI) sits at Colby House, Stranmillis Court, Belfast BT9 5RR. It issues copies of births, marriages and deaths registered here, so the certificate you already hold can stay in your drawer. A flat copy also scans better, and the scan is what the translator works from.