"Sugar good. Planet is sugar. Sorry bye". But translated into firing of neurons within the fly brain. Of course there is that concept of other and self that the fly does not have. But this might be more successful with monkeys.
Your other point about motivation to describe their purpose still stands - but the point about there being too limited similarity between conceptions of the world to convey meaning between species - that doesn't work for me. They are situated in the same universe, and it's very likely that there isn't a qualitative difference between their intelligence and our own. Intelligence must be a universal law, something that falls out of the correct interpretation of thermodynamics in open systems.
Interdimensional aliens might have a more varied purpose I suppose, but then their actions wouldn't be intelligible to us at all. They might decide to convert half all life on earth into the opposite chiral form, because reasons. Or rather because there is some unknown mapping between chirality in this plane to the goals within another plain. The chirality of these biological forms within these dimensions being but the lower part of higher dimensional things which are subject to the motivating forces of higher dimensions. Although it's much more likely that any changes would not be coherent at all in our perspective of reality. The purposeful actions of other beings within other perspective frames of totality would more likely look like random thermal/quantum fluctuations within our perspective. There I solved quantum randomness for you.
Interdimensional aliens might have a more varied purpose I suppose, but then their actions wouldn't be intelligible to us at all. They might decide to convert half all life on earth into the opposite chiral form, because reasons. Or rather because there is some unknown mapping between chirality in this plane to the goals within another plain. The chirality of these biological forms within these dimensions being but the lower part of higher dimensional things which are subject to the motivating forces of higher dimensions. Although it's much more likely that any changes would not be coherent at all in our perspective of reality. The purposeful actions of other beings within other perspective frames of totality would more likely look like random thermal/quantum fluctuations within our perspective. There I solved quantum randomness for you.