For me there’s two separate participants, a ‘talker’ and a ‘listener’. My mind identifies more with the talker, because that’s the one that has agency. Since there are two participants, both of which are me, I talk in 1st person plural (‘we’ve got to do …’, 'we thought about this earlier’). I stopped being afraid of being alone after I started having an internal dialogue around the age of 11, since having a second participant in the conversation meant I was always in company.
Edit: Wow, looks like there’s a lot more diversity in this than I was expecting
For me, well its a pre-verbalization of anything I am about to do or say.
Even typing this out I am speaking each word.
If I am getting into bed, I think “I need to do xyz”.
sometimes its inquisitive, such as when I debate over choices ranking them over each other, or when I am processing what someone says or does.
“Why did they do that? It could be this or that”.
When I was younger I had developed a minor personality split in order to compensate for neglect and bullying. They were nice to talk to, and helped me processs emotions and feel not alone. They merged back into my main personality sometime in highschool.