Is a glossary needed in a translated-novel? or I would only need to put the translation of the native words under the brackets?
If you have so many unfamiliar or questionable terms that you think the reader will need both original and translation, by all means add a glossary. More information never hurts. As long as it's in the back or front matter so the reader can choose to read it or not (that is, it doesn't interrupt the flow of the story), I say add it.
You should also consider a third alternative. Is there a character in your story who will have the same difficulty as the reader with the "foreign" words? Having a piece of dialogue that makes the meaning clear is usually preferable to an (intrusive) in-text gloss.
As an example someone might say When you call that a keris, is that any dagger or a special kind for ritual use?
I'd say first, can you just translate the words in the text and not give the original? Like in the example you give in the comments on Fortiter's post, why not just write, "Toward the beach, there was the village hall that performed a ceremonial dance every evening" ? (Or more likely, "... where a ceremonial dance was performed every evening". I doubt that the hall danced, it was more likely people in the hall.)
Is there something about a "banjar" that is not captured by the English phrase "village hall", AND that is important to the story? If not, there's nothing gained by including the untranslated word. Note the "AND" in that sentence is important. It is a classic sign of a bad story teller that he includes all sorts of details not relevant to the point. I'm sure we've all heard someone trying to tell about some personal experience that could potentially be very interesting to the hearer, who says something like, "... and when I heard that your brother had been in an accident, I quickly put on my shoes and headed out the door ... and, well, it wasn't really shoes, it was sandals, are sandals considered shoes? They're sort of like shoes, but I think of shoes more as things that have a top to them and ..." And you find yourself wanting to scream, "Get to the point! Was my brother hurt or not? How is he? Where is he now?" So if you say, "well, a banjar isn't just any village hall, it has such-and-such characteristics". This might be very important in the total context of the culture, but does it matter to the story? If not, then the reader doesn't care.
A certain number of untranslated words can add flavor. This is especially true if the word conveys something of the feel of the culture. Again going to your example, I probably would write "Kecak dance". The word "dance" tells us what it is so you don't necessarily need any futher information. The use of the untranslated word gives the impression that it has some special significance, that it is not just any dance, but something with ritual or cultural significance. If it matters, explain further.
And the easy, cheap answer: I've read translated stories that include footnotes for words that the author considered difficult to translate or valuable to include but whose meaning was not clear in context. Like writing "banjar*" and then at the bottom having a footnote that say "A village hall used for ... with ...".
I'm reminded of an interview I saw once with an American woman who had written a humor book that was being marketed in the UK, and she said that they had added a glossary to explain her Americanisms to a British audience. For example she made a reference to being "stuck on a cloverleaf", so in the glossary they defined a cloverleaf as "an interchange on a motorway in the shape of a four-leaf clover". She read a brief excerpt that was basically one joke that referred the reader to the glossary three times. And she wondered, by the time someone reads the joke, and then looks up all the words in the glossary and figures out what she's talking about, are they going to laugh, or will they just say, "Oh. I wonder why she wanted to do that." My point is that you can lose a lot of the punch of a humorous, emotional, or dramatic statement if the reader has to look up all the words before he understands what you are saying.
The novel I am translating is set in Egypt, so there are often Arabic phrases and sentences. The original uses footnotes to translate them. I find that pedantic, so I use glosses to make sure the meaning is clear, as in: "Chukran," he thanked him. Then I have a glossary of Arabic phrases as the end, so a curious reader can find all the Arabic with translations. How does that sound?