I often "talk to myself" when I'm alone in my apartment, mostly in English - even though I'm French - and mostly for my own pleasure (so it's not the exteriorisation of an "interior monologue" because I don't tend to have "interior monologues". I don't naturally talk to myself internally. But my thought processing is rather peculiar...) - for the artistic and poetic use of language. Accessorily, it helps my vocal chords not to atrophy (if I didn't telephone to my relatives after my lessons at university, I would only say two to ten words a day!). And I also read aloud my writings (in French), à la Flaubert. I often did it last year, when I was an intern, and I think the neighbours (happily I didn't have a roommate) believed then I was genuinely talking to myself, but in a rather strange way (while back then I told myself out of talking alone, which was kind of frustrating).
Oh, also, when I'm at home, I tend to sing out of happiness, when I'm alone.