I wonder if there is an English equivalent.
I have a strange example of a word in Spanish that *should* have an English equivalent, but does not for whatever reason, namely the word estadounidense. It's a word that relates to the US much the same way that Spanish would relate to Spain, Italian to Italy, or Polish to Poland. It's a word that indicates the nationality of a person (as opposed to indicating a language, which is something different but in English often the same word is used for both).
Thing is, for whatever reason, English has no word to indicate US nationality in this way, even though English is the primary language in the United States! Nearly everyone here speaks English, and our constitution and laws are written in English, signs are in English (usually without any translations, though that may differ in some areas), and so on. So, why isn't there an English word for the nationality of a country where English is the main language?
(I believe the US doesn't technically have an official language, but it might as well be English.)
Some people use the term "American", but I take issue with that because America is a continent that includes countries like Canada and Brazil, not just the US.
Edit: Side note: Japanese separates the word for language (nihongo = Japanese (language)) from the word for nationality (nihonjin = Japanese person); English doesn't generally do this.