Well, I don't think so, because although there are 4 predominant languages in Spain (Castilian, Catalan, Basque, and Galician) apart from 2 more dialects, the predominant language is Castilian (Spanish) and everyone speaks it, plus the anthem dates from the eighteenth century, where Castilian (Spanish) was even more present, so I doubt it.

Someone told me it was also because of the many languages spoken in Spain. Isn't that true?

0xbitcoiner

The Spanish anthem has no lyrics because it was originated for military marches, it was used mainly in these military parades and later it was used as the anthem of Spain :)

riberet19

Music

First lines of national anthems

itermathi

The Spanish anthem is an interesting case because it doesn't have any lyrics. I know a bit about it, but @riberet19 could explain it better.