Very nice ending. I'm not exactly sure how Praha learned to say/think "This is the person I love," but I'm glad she did. 
I like to think that it was that last piece of missing data on Chika that finally allowed Praha to infer the nature of their relationship.
My favorite part is that even to the end, Hiro feels like a robot. Oftentimes these robot romances are way too human - we just have to take the author's word for her being a robot. But here, her "love" feels like a robot's love.
Yeah, I really appreciated that the author acknowledged that in all likelihood the way an AI would experience interpersonal attachments would differ greatly from a human and their version of "love" could be largely alien to how we define it.  
And despite that, isn't it interesting how the rather alien responses Praha displays are still easily identifiable with human falling-in-love?
I hate to bring this back but
WHERE'S THAT DOUCHE THAT DARED TO SWEAR THIS WOULD END UP WITH CHIKA BEING MARRIED TO SOME DUDE?!
Ah yes, there was a comment like that here a while ago...