In Spain — my country of origin — most people speak Spanish. However, there are other languages that have been spoken for centuries, such as:
Aranese (approx. 5000 speakers)
Basque (approx. 750 000 speakers)
Catalan (10 000 000+ speakers)
Galician (2 500 000+ speakers)
Although most Spaniards understand Spanish, it may not be everybody's preferred language. That is why you must consider whether you also need to translate your message into some of those additional languages.
Spain's sole official language is Spanish. Additionally, the languages mentioned above are co-official in certain regions.
From right to left: Galician (blue), Asturleonese (darker green), Spanish (lighter green), Basque (gray), Aragonese (yellow), Aranese (red), and Catalan (orange) — Image credits: FogueraC at Wikipedia
Spanish was the language I first learned at home in Zaragoza — my birthplace. It is the main language I use with my family.
Although Catalan was not my first language, I studied it and adopted it as my primary language during the 15+ years I lived in Barcelona. This language is co-official in the Balearic Islands, Catalonia, and the so-called Valencian Community (where it is officially known as Valencian). Catalan is also the sole official language in Andorra — an independent microstate located between Catalonia and France.
Because I lived in Galicia in the 1990s, I studied the local language at school. Even though I cannot speak or write Galician anymore, I still can read and understand it. It has been helpful to build my foundation in Portuguese since Galician and Portuguese used to be (and may still be considered) the same language.
Then, there is Aranese — a variety of Occitan — which is spoken in the Val d'Aran (northwestern Catalonia). Like Galician and Portuguese, Catalan and Occitan share a common past. Therefore, most Catalans may understand Occitan. I know I can understand at least its written form.
Finally, Basque is official in the Basque Country and northern Navarre. Unfortunately, I cannot understand it because it is unrelated to any other language (language isolate). Only those who study it can understand it.
And last but not least, there are other spoken languages in Spain that may not be official but are recognized to a certain degree (e.g., Aragonese and Asturleonese).
If you need English into Spanish or English into Catalan translation services, feel free to contact me to discuss your needs!