Naturalisation and citizenship in Spain

Unless you are a national of a former Spanish colony (2 years) then you will need to live in  Spain for 10 years before you can apply, and only such nationals may retain their former nationality.

You will need really good Spanish and the test has in the past few years been toughened considerably.  One needs an in-depth knowledge of Spain, it's history and culture. I know one guy who was asked, "What if the fine for urinating in the sea at Benidorm"  !!!!!    Why would anyone know that?

Good luck

Spanish citizenship means free movement and the right
to work in any EU country (as well as applying for benefits)
so of course they have to be strict.

We're already inundated with immigrants in Sweden