Step-by-step deduction
We startStart from the bottom:
Now there's lots of other stuff to be filled in around those long words on the left, and some other deductions which lead us all the way to the centre.
Now only four 5-letter words remain to be used:
ALIEN, KOBRA, MINTA, RAKSA. All of them can be filled in directly from the single letters we have for each of them.
And all that's left is 3-letter words, which we painfully fill in using whatever deductions we can use.
Firstly NIP, KIM, PIA, OEK in the lower left (only one word left beginning with N, and the rest falls into place).
Then BEL, BRI, TEA, TUA in the upper left (only one word left ending with L) followed by IUR, AIR, RIO, HBO in the extreme top left (only one word left with U in the middle).
Then RAI, ALI in the lower left (only one word left beginning with R). The word beginning with BA could still be either BAK or BAR, but there's no other word ending with AR, so it must be BAK and IAK.
Finally QNF, QNT, BNI, BAR in the extreme bottom right.
Final solution
I need to go now, so I'm posting my progress so far and will come back to this an hour later to finish it For the thematic hidden messages, I defer to Gareth's superior knowledge of Indonesian Indonesian puzzles :-)