Certainly, I don't expect the average English only speaker to be able to properly pronounce Gaelic, Polish, or Vietnamese words, or frankly even obscure English

Certainly, I don't expect the average English only speaker to be able to properly pronounce Gaelic, Polish, or Vietnamese words, or frankly even obscure English words by sight. The results are likely much better than random texts using cyrillic, greek, arabic, hangul, etc. Otoh, If they're typists, I expect they can likely type them into a search, probably sans diacritics, but that's likely good enough for searching or looking through a translation dictionary. Greek and Cyrillic may share enough symbols that a latin script user can make due with an onscreen keyboard or a dictionary with great effort. But a completely different script would need even more effort.