http://www.travelexpertguide.org/forum/Latin-America/Getting...

A marriage certificate is a legal document that allows two individuals to wed, or proclaims them as a legally married couple. In most areas, a couple must obtain a marriage license prior to the ceremony. After the event, a marriage certificate is usually signed by the newly married couple, as well as the person who performed the ceremony, and by any official witnesses.

Some states incorporate the marriage certificate with the marriage license to create a single document. This is typically then resubmitted to a court or a government office, so that the couple can obtain an official marital document. This is then used as proof of the pair's status as a married couple.

HTH

my first thought

Or perhaps "public act of marriage" or just "act of marriage", but I think both these could lend themselves to misinterpretation, since in this case "act" means a document not an action.

I think it is difficult to find the right term here, and it is perhaps significant that in the advice the US Government offers its citizens on marriage in El Salvador, as quoted by Trujaman in his reference, the term "Escritura Pública de Matrimonio" is left in Spanish.

As to exactly what this document is and says, this can be seen from the template ("Modelo de Escritura Pública de Matrimonio") available at http://www.salvalex.com/en/templates--forms/11-otros-formato... . It is a statement by a notary, recording the actual process of the marriage. In El Salvador, this is necessarily a civil ceremony; you can have a church ceremony afterwards as well if you want.
I won't reproduce the text, because this web page won't allow you to copy bits and it would take too long to write it out by hand, but the notary states how (s)he established the contracting parties' identities, saw their birth certificates, confirmed their consent, heard their vows and declared them husband and wife.

Once the couple have this escritura, as the US Govt webpage says, they can use it to obtain their partida, their marriage certificate.

So this escritura is not a marriage certificate; that is the partida, which comes afterwards. Nor, although it records the marriage, should it be called a marriage record or record of marriage, since that term customarily means a certificate and will be misunderstood.
It is an escritura, a notarised deed, but we can't called it a marriage deed or a marriage contract, since these two terms are well established historically as denoting prenuptial agreements.

In the UN Official Document System, "acta matrimonial o en escritura pública de matrimonio" is translated "act of marriage or the public marriage registry" ( http://www.linguee.es/espanol-ingles/search?sourceoverride=n... ) . I think "registry" is not a viable translation for us here. However, "act", particularly since there are objections to all the other possibilities, could do, I think. Much further north, in Canada (or at least in Quebec), marriages can be performed by, among others, "notaries authorized to execute notarial acts", and the act is the document; you can obtain a copy of the "act of marriage" ( http://www.etatcivil.gouv.qc.ca/publications/DEP-50-marriage... )
So I propose to borrow this to cover what sounds like a comparable situation in El Salvador.

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Note added at 3 hrs (2010-12-17 20:05:40 GMT)
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Perhaps, for completeness, I should have added somewhere that it is also not a license/licence, since that comes before the marriage itself.

with the further context you have given Catherine and the reference from Trujaman I think perhaps this is the term.

The Registrar makes the record in the Registry (the office is usually called the Registry Office and even for religious ceremonies, the Register must be signed by the couple before two witnesses and the official Registrar (which can be the person, including a priest or notary who performs the ceremony) so that the marriage is considered legal.

For example, in France a couple who want to have a religious ceremony must also go to the Registry Office to have the marriage legalised. In other countries, as I've said, the officiator, priest, minister or layman can be the Registrar but the book must be signed.

There are two sets of Birth, Marriage and Death indexes in the UK; the original indexes held by the local register offices and a secondary index created by ...
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Note added at 2 days3 hrs (2010-12-19 20:27:42 GMT)
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A civil ceremony should be held (within 60 days of receiving the birth certificate or Escritura de Edad Media) and the couple should sign the Escritura Publica de Matrimonio in the presence of two witnesses. The chosen official will ask the bride which last name she will take at this time. The chosen official will be responsible for entering the marriage in a Duty book and send a photocopy of the entry to the Salvadoran’s original city hall (place of birth).

Immediately after the ceremony the public notary should register the Escritura Publica de Matrimonio at the Salvadoran’s City Hall and give two copies to the respective married individuals. The City Hall’s certification will convert the Escritura into a Partida de Matrimonio.

...Salvadoran law requires that the couple choose one of three patrimonial (prenuptial) regimes. 1) Separation of assets; Each one keeps what is theirs at the moment of the marriage 2) Participation in utility; each individual keeps its pre-marriage assets, however the couple must divide equally the properties that appreciated during the marriage; 3) Division of Assets; divide all assets (initial and accrued) equally at the end of the marriage. The public notary will enter the chosen patrimonial regime in the marriage license.

The law applies in all Salvadoran jurisdictions...

El Salvador's marriage laws are significantly different than those in the U.S. Primarily, it is important to note that, by law, the couple must have a civil ...
sansalvador.usembassy.gov/marriages.html - Cached - Similar