RobH_en_tn/exo/04/10.md

have never been eloquent

"have never been an excellent speaker"

I am slow of speech and slow of tongue

The phrases "slow of speech" and "slow of tongue" mean basically the same thing. Moses uses them to emphasize that he is not a good speaker. (See: rc://en/ta/man/translate/figs-doublet)

slow of tongue

Here "tongue" refers to Moses' ability to speak. Alternate translation: "unable to speak well" (See: rc://en/ta/man/translate/figs-metonymy)