Hebrew was a Canaanite dialect. Akkadian was the language of Mesopotamian peoples (Babylonians and Assyrians) that went through several stages until it finally died out towards the Common Era.
Being closer to the original Proto-Semitic language that gave birth to all Semitic languages, Akkadian only featured four vowels (a, e, i , u); had a strong preference for /sh/ instead of /s/; and tended to end nouns with the vowel u.
In Canaanite dialects, the end u in nouns was dropped; the hard k became pharyngeal in some instances (like ch in loch, or Bach); the hard b also softened in some cases, to /v/; and—due, perhaps, to influences by non-Semitic, Indo-European nations, such as the Hittites and Grecian Sea People invaders—a vowel shift occurred that introduced all five basic vowels (a, e, i, o, u) into the language. As a result, words that had the same consonantal root as Akkadian, usually sounded quite different. Thus:
- akal [food] in Akkadian > okhel in Canaanite
- libbu [heart] > lev
- shipru [missive, letter] > sepher
- mahiru [price] > meḥir
- shataru [bill] > shtar
In addition, many words changed in meaning—e.g.:
- siklu [wise man] > sekhel [wisdom]
- emutu [family, society] > amit [colleague]
- mazzaztum [star position] > mazal [luck, fortune]
The end result is that the Akkadian and Hebrew/Canaanite were not mutually intelligible in speech, but partially intelligible in writing, if the same script was used (such as the Canaanite script, which was ultimately adopted by the Assyrians and then the Babylonians). In that regard, the relationship is very similar to that between Arabic and Hebrew, today.