OK, so playing the Imperial campaign, I noticed some glaring mistakes in the translations, specially on the names:
Some faction and subfaction names aren't translated at all:
Tyranid/Tyranids => Tiránido/Tiránidos
Necron/Necrons => Necrón/Necrones
Blood Angels => Ángeles Sangrientos.
Dark Angels => Ángeles Oscuros.
Iron Hands => Manos de Hierro.
Space Wolves => Lobos Espaciales.
Alpha Legion => Legión Alfa.
Black Legion => Legión Negra.
Death Guard => Guardia de la Muerte.
Iron Warriors => Guerreros de Hierro.
Thousand sons => Mil Hijos
Piratas Orks (this one belongs to the "spanglish" realm) => "Orkoz Korzarioz" or "Korzarioz"
"Corsario" is technically correct for Corsair, but feels odd in singular form, would be better if it was translated as "Corsarios".
Now, the naming structure of the fleets (at least the imperial ones) are wrong:
For example, Spire's fleet is named "7ª Gótica Flota de guarnición", "flota" or fleet should go before the fleets actual name, so it should be "7ª Flota Gótica de guarnición".
Another one is called "15ª Bastión Grupo de combate", it should insted be "15º Grupo de combate de Bastión".
Lastly, "16ª Ultramarines Flota de guarnición", which should be "16ª Flota de guarnición de los Salamandras". This one might be wrong even for the english version as it gave an Ultramarine name to a Salamander fleet.
As for the ships, they are all untranslated but I think its reasonable to mantain them as such, they are consistent in their naming and sound cool.