There was a very gradual shift to more and more people switching to Arabic (and converting to Islam) over centuries but no, there was no official language. What few Arabs there were spoke Arabic dialects, the Berbers spoke Berber, and people of local stock continued to use Romance language varieties collectively referred to as the Mozarabic language (with the Iberian Jews also keeping the use of Hebrew). This question gets asked quite frequently - you may want to check out [this recent thread] (https://www.reddit.com/r/AskHistorians/comments/53td8u/why_is_there_little_effect_on_the_spanish/), for instance.