Would the plain form of a verb usually be translated as future tense?

In a recent question I asked, this example sentence was offered:

映画を見る。 (I will watch a movie.)

What struck me about this was that the translated version was the future tense.

However, I always thought the plain form of a verb was tense-less.

映画を見る。 I watch a movie.

When I think about it, though, if the plain form is without tense (or at least not future tense), then it wouldn't really be used much except in answer to a question:

Q: 退屈しているときには、通常に何をしている？ (What do you usually do when you're bored?)

A: 映画を見る。(I watch a movie.)

Maybe I just have it all wrong.

Is the plain form usually assumed to be future tense? Or at least an expression of intent?

Answer

I imagine most grammar texts break Japanese tenses into past and non-past. So the plain form can be used to describe something you will do (once) in the future as well as something you do on a regular basis or something that tends to happen. Context tells you which is meant:

明日【あした】は映画【えいが】を見【み】る。 Tomorrow I will watch a movie.

毎週【まいしゅう】金曜日【きんようび】に映画【えいが】を見【み】る。 Every Friday I watch a movie.

今夜【こんや】はレストランで夕食【ゆうしょく】を食【た】べる。 Tonight I will have dinner at a restaurant.

夕食【ゆうしょく】をいつもレストランで食【た】べる。 I always have dinner at a restaurant.

In English the auxiliary "will" marks the future tense, but Japanese doesn't discriminate between the two usages shown above, so the same plain form 見【み】る and 食【た】べる can satisfy both cases.

Your Q&A example is an instance where the non-past (plain) form of the verb shows a habitual action (I'm going to edit it a bit):

Q: 退屈【たいくつ】なときは、何【なに】をする？ What do you do when you're bored?

A: 普段【ふだん】は映画【えいが】を見【み】たり、漫画【まんが】を読【よ】んだりする。 Usually I watch movies or read manga.

So when you have a verb all by its lonesome without anything to tell you which of the two cases it fits into (like 映画【えいが】を見【み】る), you kind of have to guess. I usually fall back on translating it into the English future tense unless I have reason to believe it's better left as English present.