Thread: В следующем месяце мы собираемся навестить своих друзей!

Now I see what you mean
But you do not even imagine how deep your question about "собираться" vs "to be going to" is! Your question touches some basics of the "linguo-cultural" relationship. The general idea is that every language reflects some specific view of some culture. There are some words and expressions which exist in language A and have no exact equivalents in language B because they are somewhat "culturally specific" words.

To be brief, the English expression "to be going to" has NO exact Russian equivalent. Of course, there are some ways to express your intension to do something immediately. For example, you can say:
"Я буду купаться прямо сейчас" - I will swim right now.
"Давайте искупаемся прямо сейчас!" -Let's swim right now!
"А сейчас я хочу искупаться" - And now I want to have a swim.
etc.
It depends on a specific situation.
However, there is no fixed expression for "to be going to" in our language.

On the other hand, "собираться" is a very Russian verb. It has no exact equivalent in English.
Yes, when I learned English at school, we were taught to translate "to be going to" as "собираться". We had to learn this expression since it is very frequent in English. But the teacher did not explain us all the nuances.

That is not my own thought. I read a very interesting article which explains the "linguo-cultural" relationship in general, and discusses the verb "собираться" in particular. Unfortunately, the article is in Russian. I can find it and I can try to translate it into English, if you are interested in this subject.

Shall I?

I always internally translate "собираться" as "preparing to...", which has the certainty of "going to..." without the implied immediacy or imminency.

It's not precise, but it's usually closer in meaning.