I wouldn’t start a conversation with a stranger about their baby’s name. But I have complimented people when I first meet them and learn their kids’ names (I always ask).
I’m 14, so it would be a bit awkward for me to do that unless I was alone i think. Idk that’s just my viewpoint. So I would if I was alone.
If a stranger brings up the subject their children when I’m talking to them then I might ask what they’re called (especially if said child is with them at the time) and compliment them on their choices, even if I’m not keen on them.
I mainly do it because getting a compliment on my own child’s name makes my day so it’s nice to do that for someone else! 
It’s actually kind of a problem. I like a lot of names and can usually find something I like about any name. So I do this A LOT.
Not usually, but I was served by a [name]Flora[/name] in a shop the other day and I simply HAD to comment! I just said I thought her name was beautiful
I’m a bit of a mumbling mess in public (put me in a crowd of people and I’ll probably make a few sputtering references to an episode of Friends or something then back into my corner) so I don’t comment on names. Should I receive a spine, I would probably say something if a name was especially stunning.