As someone who at one time spoke fluent Bosnian/Croatian/Serbian, I can confirm that "spomenik" can be (and sometimes is!) translated as "memorial". Indeed, the root of the word is a verb that in its archaic sense can mean "to remember", as does the verbal root of "memorial". Furthermore, "spomenik" can also be translated as "monument".
So while the word often is used in the context of the WWII socialist memorials, the word in fact just means "monument" or "memorial". For example, here's an article using the term for a memorial to veterans ("defenders"), specifically those who died, from the 1991-1995 Croatian War for Independence: https://pakrackilist.hr/spomenik-hrvatskim-braniteljima-dovr...
I don't completely disagree with the author's idea to use the original term to add some local color, but it's not a special term, just one of the general terms used for memorials and monuments. A related term, "spomenica", is also frequently used, but I'm not sure about the nuances between these two terms.
I'm sure a native speaker could fill us in.