You misunderstand. Other regions have their own language dubs as well, not just text. The Spanish version has a Spanish dub, the French version has a French dub, Italian version has an Italian dub, Japanese version has a Japanese dub and you get the idea. The Ghost voice in their respective languages are, to my knowledge, not changing voice actors. As a result, it wouldn't make sense to do a tribute to an English speaking voice actor only and put it in all regions of the game where the voices are different languages to begin with. And to do it for only one version is impractical from a development standpoint because they would have to keep it separate from the other versions on purpose which I imagine would be somewhat of a hassle but that's just a guess.