What is the translation methodology for the Nueva Versión Internacional (NVI)? I'm wondering about what sources were used for the NVI.  Was it translated from from ancient Hebrew-Aramaic and Greek manuscripts?

All I can find online is that the translators "follow[ed] the NIV tranlation [sic] principles," meaning that "the translation process sought to preserve the original language while taking into account the target language as well" (NVI version information).

I would assume that means that the NVI is in fact based on ancient manuscripts, since the NIV was, but it's unclear.
Yes, it was translated from the ancient manuscripts.  The preface of my copy of the NVI is also available online, &quot;Historia de la NVI&quot;.  I'll quote and translate key sections of that article here.  First, a summary:

La traducción se hizo directamente de los textos hebreos, arameos y griegos en sus mejores ediciones disponibles.

The translation was made directly from the best-available editions of the Hebrew, Aramaic, and Greek texts.


Later, it goes into more detail on the NT:

La traducción [del Nuevo Testamento] se basa en el texto crítico griego actual, que da preferencia a los manuscritos más antiguos. Cuando se dan diferencias sustanciales entre este texto crítico y el texto tradicional conocido como Textus Receptus, la lectura tradicional se incluye en una nota, como variante textual.

The translation [of the New Testament] is based on the current critical Greek text, which gives preference to the oldest manuscripts.  When there are substantial differences between this critical text and the traditional text known as the Textus Receptus, the traditional reading is included in a note, as a textual variant.


And on the OT:

La base de la traducción [del Antiguo Testamento] es el Texto Masorético (TM), pero en algunos pasajes se ha aceptado una lectura diferente. En estos casos, la nota incluye entre paréntesis la evidencia textual (principalmente en las versiones antiguas) que apoya tal lectura; luego se indica lo que dice el TM.

The basis of the translation [of the Old Testament] is the Masoretic Text (MT), but in some passages a different reading has been accepted.  In these cases, the note includes, in parentheses, the textual evidence (mainly in the oldest versions) supporting that reading; afterwards it indicates what the MT says.


Another important thing to note is that the translation includes a moderate revision of personal names:

Otra diferencia entre la Nueva Versión Internacional y las versiones tradicionales tiene que ver con la onomástica hebrea. En el caso de nombres propios bien conocidos, esta versión ha mantenido las formas tradicionales, aun cuando no correspondan con las del hebreo (p.ej. Jeremías, aunque el hebreo es Yirmeyahu). En otros casos se ha hecho una revisión moderada para que los nombres no solamente reflejen con mayor exactitud el texto original (p.ej., la consonante jet se ha representado con j en vez de h), sino también para que se ajusten a la fonología castellana (p.ej., se ha evitado usar la consonante m en posición final).

Another difference between the Nueva Versión Internacional and the traditional versions has to do with Hebrew onomastics.  In the case of well-known proper names, this version has kept the traditional forms, even when they do not correspond with the Hebrew (for example, Jeremías, even though the Hebrew is Yirmeyahu).  In other cases a moderate revision has been made so that not only do the names more exactly reflect the original text (for example, the consonant jet is represented with j instead of h), but also to adjust them to Spanish phonology (for example, to avoid using the consonant m in the final position).