OK, as I have promised:

The article’s name is «Картина мира, нарисованная языком» (The world picture as it is painted by the language). Its original version (in Russian) is available here: Наука: Картина мира, нарисованная языком. Please have a look at it, even if you cannot understand Russian: there are some funny pictures illustrating some words (including «собираться»).

The whole article is quite long, and I have only translated its part where it comes to the specificity of the verb «собираться».

I am not so good in text translation, probably someone else could do it better. So feel free to correct me and to ask if something is not understandable.

I have also provided some grammar comments to make things clearer. The article itself is more for Russians who learn foreign languages.

…

«Собираться»

When you say «Я собираюсь изучать английский язык» (I am planning/intended to learn English) to your friend, your friend understands it well that you are not currently learning English, and there is even no guarantee that you will ever start learning it. Russian «собираться», Shmelyov explains, is a kind of an important concept which carries the idea that a person has to “mobilize his inner resources” prior to doing something.

It might seem there is no significant difference beween «планирование» "planning" and, say, «намерение» "intention". However, it is completely impossible to imagine a situation when we were "planning, planning something" «мы планировали, планировали» but finally do not succeed in "getting it planned" «так и не запланировали».

On the other hand, if we «собирались» (past tense imperfective!, i.e. we were in the process of «собираться») to do something, that could really be the case: that is quite natural for us to say that a person «собирался» (past tense imperfective again!) to do something, but did not «собрался» (past tense perfective – i.e. did not succeed in «собираться»), - Shmelyov says. But if a person finally «собрался» (past tense perfective – i.e. he succeeded in «собираться»), that nearly guarantees he has almost "done" it!

Other words, the process of «собираться» in the view of the Russian language, is a more important part of an action than the action itself. Linguists think, it is probably due to our wide spaces. Unsurprisingly, when we are getting ready for a trip, we namely "gather the things" (собираем вещи), as compared to Englishmen and Frenchmen, who "pack them" (пакуют их). Of course, we are packing them as well, but it is more important for our language that we have everything "gathered". As for packing – we will surely have time for that.

The distance between the English "I am going", which is usually translated into Russian as «собираться», and the corresponding action is much shorter. If you imagine a Russian sentry on guard who is crying something as «Стой, я собираюсь стрелять!» - "Stop, I собираюсь to fire!" to a stranger, the stranger will hardly be frightened – it is not obvious when that "scatter-brain" finally «соберётся» (future perfective – will succeed in «собираться», will get ready to fire). But the English "I am going to fire!" means you are already aimed at, and the cock is raised.

/My comment: of course, it’s impossible to imagine a sentry on guard saying «Стой, я собираюсь стрелять!» - it already sounds funny. In reality, he would say something like «Стой, стрелять буду!» (Stop! I will fire!) or even «Я стреляю!» (I am firing!) to accentuate his resolution. «Собираться» is certainly not an option in this context/

But when I tried to explain the meaning of the Russian verb «собираться» to Kieshi Oguri from Japan, neither me nor my interpreter could manage it at all. Oguri kept shaking his head and shrugging his shoulders. What can we do? – His world picture is different!