Broadly, INFPs seem to find INFJs somewhat judgmental and over-serious (as someone said already) and that they hold others to higher standards than they hold themselves. All of which I admit I can see some truth in. (in some cases at least)
INFJs don't get much love around here any more though.

It makes a change from the days when people were like "INFJs are psychic wonder-gurus whose love and caring is second to none." (that kind of thing is really annoying too)
I tend to think that INFJs and INFPs, or even xNFJs and xNFPs, tend to reach similar conclusions and to think along the same lines in many ways, but the process and communication trip each party up. The Portuguese and Spanish analogy was quite good. Languages which are similar but different, and thus even more frustrating in some ways.
I can't remember if it was on this forum or elsewhere but I read something about xNFJ and xNFP which I thought was nice. xNFJ might find xNFP flaky, inconsistent etc, and xNFP might find xNFJ too rigid, judgmental etc - but neither will think the other is "weird". And these are types who often get called weird by others. And I think there's a lot of truth to that, and there's something good in it.
EDIT: Sorry, I shouldn't really butt into a thread for INFPs

But I do find this subject interesting.