When the Moors conquered Spain did Spaniards already speak Spanish? Or were they speaking a different language like Latin?
They were speaking Latin
In 711, the Moors took over Hispania. While Vulgar Latin was dominant, due to the influence of the Moors, it took on a different form, integrating Arabic and forms of a related dialect called Mozarabic. Arabic was the most influential language in the development of Spanish; it is estimated that approximately 3000-4000 words in today's Spanish are derived from Arabic.
In 1492, Granada was defeated and the Moors were expelled from Spain. The dominance of the Castilian dialect continued to grow as the Catholic kingdoms took over most regions of Spain. Isabella and Ferdinand declared Castilian Spanish to be the official dialect. Soon thereafter appeared the Art of the Castilian Language, a work that helped shape and standardize the Spanish language.
The distinction between Latin and Spanish (or Catalan, Portuguese, French, Italian, etc.) is inherently somewhat arbitrary. These languages went through a series of stages, some of them poorly documented. Until very recently, most people would also have spoken a local variant that didn't evolve into a modern, standardized language.
What can be said is that
Latin mostly supplanted other unrelated or weakly related languages (including Basque, celtic languages, etc.) earlier and hasn't been displaced in Spain (or France or Portugal) to this day, even as some other populations (including Germanic or Arabic rulers) invaded these regions. So many people did speak a variant of Latin, however you want to call it (see also the Mozarabic language).
The language(s) spoken at the time were still very different from modern languages but also already quite different from classical Latin. Customarily, what's called Old Spanish is a state of the language that appeared several centuries later so, if anything, the language spoken in the 8th Century could still be called “Latin” but do realize it's all a gradual process.
The Iberian Peninsula was not arabized, but islamized.
Most people in Spain were Romance speakers, it did not matter if they were Muslims or Christians.
The Arabs in Spain were an elite class, like the Arabs in Iran today.
Also, there was influence in the vocabulary, by adding new words to this Romance dialects spoken in the Peninsula; even the Muslims used to write their Romance language in arabic alphabet.
Spain was not arabized at all. Had Catholic kingdoms not won the war, a big portion of Spain would be a Romance-speaking country with a majority of Muslim people.
At the time of the moorish invasion there were different ethnic groups living in what is now modern Spain. Being one of the more influent, the goths, which spoke gothic and latin mainly. Latin, in fact, was some sort of "common language" for the inhabitants of the peninsula, derived from hundreds of years of roman occupation.
During the eight centuries that the Moors were stablished in the penninsula a lot of things happened (eight hundred years is a lot of time), and keep in mind thatbthe Moors weren's occupying the whole peninsula during that much time. They conquered almost all of the territory lightningly fast, but soon started to have problems maintaining control of the northern territories. It is in that moment when, in a very slow way, some type of national identity emerges in the penninsula. This is something that will cristalyze finally with the Catholic Kings, in the 1400s, so keep in mind that it was a very long process.
During this period, different kingdoms appeared, evolved and maintained an almost constant fight against the Moors, pushing them backwards, but also coexisting with them and the people that lived under their government after they were expelled.
This is the time where Old Spanish emerges, over several centuries, a language whose base was Latin, but that was deeply influenced by Gothic and Arabic and which was also influenced by other minority languages that were spoken earlier in different zones of the peninsula and that coexisted during this extense period.
That's not "Latin"... That's a variant which belongs to the language group of so-called Romance Language(including French etc), clearly vulgar Latin mixed with local peculiarities, which differed a lot with the original/formal Latin in Roma. Also remember that Spain was dominated for a few hundred years by Visigoths(some kind of Germanic people) before the Moors. I wonder whether they were mutually intelligible at all. If people were not speaking a Romance Language when the Moor came, then how could they be speaking one instead of an Arabic language after they were gone?
Anyways such an answer could have easily been found on Wikipedia etc. isn't it? https://en.wikipedia.org/wiki/History_of_Spanish https://es.wikipedia.org/wiki/Historia_del_idioma_espa%C3%B1ol
Arabic did not great influence the Spanish language, but only secondly to Latin. Before the Roman's came, the Iberian Peninsula was inhabited by Celts and local Iberians who spoke a protoCeltic, Celtic, and indo European type language. The Roman's introduced latin which would would supplement 80-90% of the language spoken (not including the Basques). To this day, Portugal and Galician (North West Spain) are the two languages that, second to latin, have the greatest linguistic influence from old Celtic tribes who used to live in this isolated region, and some Germanic words from the Suevi. This is because this region of the Iberian Peninsula had the least amount of contact with the Roman's and was the birth place of the reconquesta, which meant Arabization was minimal and rejected.
To this day, the Portuguese language, having been descended from the reconquesta birth place in the North, retains over 1,500 Celtic words, and European Portuguese retains unique phonetic syntax separate from Spain. Spain on the other hand mostly dissolved regional variations of the vulgar latin spoken across the peninsula with Castilian Spanish
There were a lot of languages, as right now but Spain wasn't as big as today, Moors came and the Spainiards absorbed a lot of words, culture, science and concepts [things that came to English trough Spanish and trough Arabic like chess, algebra or even tuna from Arabic attun, Spanish atún] and the Spanish didin't modify a lot, just added the new words. The Spanish of that time were different that today's Spanish, mostly in pronunciation but reading old texts it can be kind of comprehensible. This started in VIII century and they were expelled in XVII century.