The word "myself" is used to emphasize that Yahweh was the one who knew about Moab's defiant speech. (See: [[rc://en/ta/man/translate/figs-rpronouns]])
Here "his" refers to Moab which represents the people of Moab. Alternate translation: "their defiant speech ... like their deeds" (See: [[rc://en/ta/man/translate/figs-metonymy]])
The abstract noun "speech" can be stated as a verb. Alternate translation: "that he has spoken pridefully" or "that he has spoken arrogant words" (See: [[rc://en/ta/man/translate/figs-abstractnouns]])