The book is one of the Time Life Great Ages if Man series, African Kingdoms. As a side question, does the aforementioned series, with 21 topics such as Age of Progress, The Reformation, and Classical Greece, and written between 1965 - 1968, still hold up or are they hopelessly out of date? I've been reading them and beyond the few mentions of stuff like "the negroe man" or "oriental" as outdated phrasing I've loved reading them, full of information and color pictures and maps, I'm having a field day.
Meroitic script itself was deciphered before WWI by noted Egyptologist Francis Griffith (Meroitic script is derived from Egyptian hieroglyphs). However language itself remains mystery. Similar situation is with Etruscans- we are able to read they text, we just can't understand what is written.
Apart from this detail- language, not the script is the problem- not much can be added. No breakthrough was achieved and- unless major bilingual text will be found- it is unlikely to happen.