Yep I don't quite understand at all. Why would Hieda need to keep on asking these questions to Yuuka if she already compiled them all into her chronicle of Gensokyo? Or maybe she is trying to finally come to an understanding with Yuuka whenever she reincarnates so as to finally have a comprehensive idea of her. Though if that is the case then she is going to continuously consult her whenever she reincarnates, however since she doesn't live for that long she wouldn't be able to reach that stage. Huh... that is actually rather depressing...
god dammit yuuka, dealing in esoterics like that, answer the damned questions. pls.
Well the way that she talks does require one to understand her on a personal level. In this way it presents her as being honest with Hieda during the interviews. If one was unable to understand the words that she says then that likely means that they probably don't understand Yuuka herself. Also since Hieda is doing this for her chronicle (I assume), it would be better that Yuuka was more incline to let her in on herself even she wouldn't get it.
Granted this does pose the problem that I said above, that Hieda wouldn't be around long enough to actually come to a proper understanding with Yuuka, with her having a more regular human lifespan (also with each reincarnation causing her to live shorter than the last). Despite this I'd still think it's better for Yuuka to have that sort of attitude when being interviewed. At least in my opinion.