I am afraid that it is easy to come with translations, but it is hard to fit them in a song.
Especialy when only minor differences in meaning are involved.
Anyway, as long as the desired meaning is "for the sake of X",
fpi is correct - with only one notice: it is an adposition, thus some noun or normalized clause is required:
"
Leru krr fpi fwa kaltxì si." or "
Krr za’u fpi fwa kaltxì si".
Without
fwa, I see "
lu krr fpi awnga kaltxì si" - "
There is a time for us", and the "kaltxì si" remains alone.
Personally, I wouldn't use
fpi, but
fte, because it seems to me much closer to the original meaning:
"
Krr za’u fte kaltxì sivi." (still maintaining 8 syllables as your original)
My preference of
fte is also based on the fact, that
fpi is to be used with a noun, while "kaltxì si" is an action.
Completely different approach is to use the adverb
nìkmar:
"
Nìkmar awnga fìtsap kaltxì säpivi " - It is the right time for us to greet each other".
- here the inclusive plural pronoun
awnga directs me to use the
fìtsap construction - we are saying hello to each other, no to someone else, and subjunctive
<iv> express the possibility of action to happen.
The worst thing in translating to Na’vi is not the unability to say something, but the choice from many possible alternatives
