Steve's book: Hitchhiking in Europe

in this part of Steve’s book the word “Spaniards” is used to refer to people from Spain. What’s the difference between this and “Spanish”.
The complete sentence is:
“With a little bit of study and reading in Spanish, and daily conversation with the friendly and talkative Spaniards, I was able to bring my Spanish up to an acceptable level.”

A Spaniard is a person from Spain, a Spanish person.Spanish is an adjective Spaniard is a noun. This is like Frenchman or Swede or Scot as opposed to French person or Swedish person or Scottish person. This is just usage.

how interesting!
In Portuguese we don’t have such a distinction. We use the same word either as an adjective or as a noun.

This is not the case for all nationalities, just for some, for historical reasons. We say Irishman, Frenchman, but an Italian and a Greek, a German, a Brazilian, but we say Dutchman, Turk. Englishman, Welshman.

But is it optional?
I mean, can I choose between saying “the French” or “the Frenchman”?