1 the Messenger of Yahweh = מלאך יהוה.   In all but two post-exilic passages (Mal. 2:7; Hag. 1:13) this phase is a technical title for Yahweh's manifest of Himself.  The Malakh Yahweh is regularly identified as Yahweh Himself, starting with its first use in Genesis 16:7.   He is the theophanic Son of Yahweh, Messiah Yeshua.  The word מלאך does not mean "angel" in the traditional sense.   It actually means "messenger", but it would not be entirely correct to consider the meaning of the phrase as a mere "messenger".  The contexts, and almost exclusive use of this phrase for a person identified as Yahweh, show that this phrase refers to the uniquely begotten Yahweh who is sent by Father Yahweh, and no one has ever seen the Father. 

2 The Messenger of the Almighty = מלאך האלהים.    The phrase means the same person as the Messenger of Yahweh.

3. the Almighty = אלהים.  "Almighty" is the nearest English meaning to Elohim.  The root Eloah means mighty or powerful, and the plural ending makes it superlative, i.e. "most" or "all".  The plural gives the sense of "the mightiest of the mighty ones", and is compactly expressed by "Almighty". The term is used in both as a title, "the Almighty" and as an adjective "Almighty", and refers exclusively to Yahweh.  When referring to false gods or judges, the plural has the normal English sense, "mighty ones".  It was thought best not to translate this term as God, because the frequent adjectival and descriptive use of the term is obscured in the translation God.

Further, it was thought best not to translate Elohim, because though the typical reader will be able to say it, the typical reader will not be thinking about its real meaning when using it, unless he or she can actually think in Hebrew.