No, it won't be rare. And that's the reason why we're NOT doing
subtitles. This is the difference between something sounding neat on paper,
but not in reality, and especially not on a TV series.

If you're doing a feature film, and only have one or two shots of aliens
talking in subtitles, for brief periods, you can do this; also if you're doing
an SF series in which you're mainly talking to humans, and only rarely among
your own kind.

But in B5, a LOT of our time is spent with our various alien characters.
And sometimes the conversation can get quite detailed, quite complex or
political. In one script, for instance, there's a 2 1/2 minute scene with
G'Kar and Na'Toth, followed by two lengthy scenes with Londo and Vir, and
Delenn and Vir. So you're talking about maybe 5 minutes here. The
conversation is very detailed, very elaborate. So are you a) going to put all
of this complex dialogue on screen, line by line, and b) use subtitles for
FIVE UNBROKEN MINUTES?

You'd kill yourself as a series. No one would stand for it, and they'd
be right. Again, not every good idea is a workable or practical idea.

jms