ba'e pe'i di'e
You are free and officially sanctioned to fake a smile. Politicians do
fake smiles. In spite of all that, a smile usually means something to
you (not in a propositional way). However that works, that's how UIs
should work.
Whenever human beings smile, we are *usually* entitled to say that they
are happy (I’m simplifying, obviously). You are wise to assume that
*some* instances of smiling are fake, but you just don't assume that
*all* smiles are fake. If you did, you'd probably end up being
considered mentally ill or something.
Whenever a Lojban speaker says {.ui}, same thing. It is part of the
Lojban Sprachspiel.^^
Whenever I feel like giving in to the temptation of thinking about UIs
in terms of truth and falsehood, I remind myself that UIs are
essentially like body language, viz. (to the ideal Lojban speaker) they
are a natural extension and, if you will, enrichment of it. Verbalised
non-verbal communication.