I have been translating a novel that is originally written in my native language into English. Considering that the book's plot is the author's experience of a life that has happened in the past, I've been using past tense. Should I use present tense instead?
Most stories in English are written in the past tense. If it happened five seconds ago, it's still past.
Occasionally writers put a story in the present tense with the idea that this will give a sense of immediacy. If done well it can certainly work, but it's unusual, and any unusual writing style tends to be distracting.
So my short answer would be: Use past tense unless there is a specific reason to do otherwise.
The best you can do, I think, is to try and pick up on the tone of the work that the original writer was trying to convey.
Since your profile indicates that you're an Indonesian/English translator, I did a little research into Indonesian verb tenses, and I think I understand your problem. While this may be an oversimplification, I've found while verb forms don't change depending on tense, the language can indicate tense using other cues, although the "tense" can still be a bit vague. (Am I correct in thinking this?)
Here are the advantages and disadvantages of various tenses:
Past tense, in English, was the most common way to write. When in doubt, it was hard to go wrong by using past tense. It created a sense of things that have happened, perhaps setting out a sense of creating a record of events - whether formal or informal. Past tense was flexible, simple, and easy to write.
Present tense creates a sense of immediacy. Present tense is a little clumsy, but the sense that events are unfolding right now as I write these words is worth effort of wrestling with language. (For example, do you need to shift tenses when somebody is telling a story? People tend to speak in past tense, how do you handle this with descriptive text in present tense?)
Future tense: (While this won't be part of your question, I'll include it here for the sake of completeness and perspective.) Future tense will be the rarest of all "viewpoint" tenses when writing a book. The problems you'll get when writing in present tense? They'll be magnified even more when you tell the reader: "This event will happen." Prose in future tense will create a sense of things that are planned to happen, even one of things that may or may not happen. This unreliability may also set out a bit of a disconnect between the narrator and the reader.
So, getting back to your book: You may find it most helpful to look at the advantages and disadvantages of various verb tenses and pick the one that most closely matches the tone and intent of the source material.
Keep in mind that what tense you use is not a decision you'll make once for the entire book: Narratives have a main tense, but characters will tell stories, talk about plans, and there may be sections that are flashbacks to other events.
Reading English books in these various tenses, observing the effect of various tenses and viewpoints, will also help you make these decisions.
This question is more complicated that it first appears! I hope I've been able to help. Good luck!