All NPCs, except guards, can be taught to talk.
All you need is a dialog record. Import one from the database, they are found under records/dialog. Copy it, and edit your copy to your liking.
Then open your NPC's creature record .dbr for editing. Under the heading 'NPC Static Dialog' set the 'DialogPak' variable to point at your dialog .dbr file.
Build your mod. The next time you play it, you will see the yellow lozenge over the NPC's head, and he will talk to you.
Step by step tutorialEdit
Click here for a step by step tutorial
See also: Talking NPC Creature