Selamat malam usage
I and a friend meet on a road. We talk then walk off in opposite directions with the knowledge that we'll meet after a few days probably.
Do we both say selamat jalan to each other, or we use a position-neutral farewell phrase? What is such a farewell phrase by the way?
Selamat jalan means goodbye, and so does selamat tinggal, but you only say selamat tinggal if they are the one leaving, and selamat jalan if you are leaving. You could say selamat tinggal, sampai jumpa lagi, which means goodbye , see you again (formal). Or if you are closer/friends you can say the informal way, sampe jumpa, bye.
Personally, I would use 'sampai nanti' (see you later) or 'sampai jumpa' in this context.
As Kohoutseks said you only say 'selamat tinggal/jalan', if someone is staying/leaving, e.g. if someone invited you to their house, the host would say 'selamat jalan' to the guests who are leaving, while the guests would say 'selamat tinggal'.
Another alternative would be "Sampai ketemu lagi", which is more informal than "Sampai jumpa" or "Sampai nanti".
Even more informal is "dadah" (bye-bye). Sometimes people also say, "Yuk, 'Name'". And of course, Indonesia being the largest Muslim country, many Muslims also use "Assalamu'alaikum" as a farewell phrase.
I wonder if the phrase "selamat tinggal" is still used. I rarely hear it outside books. "Selamat jalan" has more use, but I hear it most often when someone's leaving on a long journey. For example, if you're going to your hometown for the holidays, your neighbor may wish you "selamat jalan".