Generally speaking, a legal authority has to stamp and verify a translation to make it official. Yet, the process for this broad term varies from country to country because of different legal systems.
Firstly, to certify a translation, the translator must attest that the translation is true, complete and accurate to the original document. The translator will stamp and initial each page as a watermark to avoid tampering or misuse. Certification seals can be purchased which certify their work. The translator has to be a part of a Qualified Translation Association such as MITI, ITI or FITI to be eligible for the front-page certificates. This process is very similar in Portugal with a certification validated from a Law Society Member.
An Apostille is used on official documents such as a birth certificate to verify its legitimacy and authenticity which allows it to be accepted in any of the 117 countries part of the 1961 Hague Apostille Convention. A Notary Public can seal a translation with an Apostille stamp, assuming that the original document has one. In the UK, the Foreign Commonwealth Office (FCO) is the competent authority for issuing Apostilles. The Attorney General’s Office is the competent authority in Portugal.
Finally, notarised translations refers to a translation that has received a declaration from the Notary Public and the translator. Subsequently, they are used to make the translation official for overseas use. The Notary’s signature must be a Qualified ITI member to be able to endorse the translation’s quality.
It is worth mentioning that sworn translators do not exist in the UK. In civil law countries such as France, Spain and Germany, a translator will need a degree or a specific translation qualification to be able to produce sworn translations. Government authorities have to appoint and recognise these translators in order for them to generate certified, sworn or official documents.