Spanish is a language from old Terra. It is one of a number of languages found on that World that were derived from Latin, and had become one of the most widespread languages of pre-spaceflight times. The language is, in its current form, still one of the predominant languages of Terra and spoken at home across that world.
At the time of the Solomani spreading to the stars, Spanish was one of the major languages of Terra and while never an official language of the subsequent Rule of Man was one of the more widespread languages spoken across the Worlds settled by the Solomani. There are many loan words from old Spanish in modern Anglic - especially names.
With the explosion of the language onto many worlds, and subsequent disruption of interstellar travel created by the Long Night, Spanish has fragmented into a number of distinct dialects and derivative languages, much as Latin split into multiple dialects and languages (including Spanish) in pre-spaceflight times.