So in which (human) languages do programmers (a) entirely use their own languages with its own native technical terms; (b) drop English terminology into sentences in their own languages; (c) switch entirely to English when talking about programming?

My one data point of amusement: I once worked in Hong Kong (a Cantonese-speaking city) with a team which had outsourced part of its project to Shenzhen (a Mandarin-speaking city). In HK Cantonese, people usually use Cantonese words for simpler technical terms like "web page" or "hard disk", but more complex ones like "dual boot" or "buffer overflow" would be in English. In Mandarin, and also Cantonese as spoken in the mainland, they use almost entirely Chinese terms ... or at least a lot higher proportion than in HK Cantonese. (A lot of those terms, of course, are just calques from English).

Now, the HK guys could speak passable Mandarin, and some of the Shenzhen guys could speak okay Cantonese (though not much English). So if the two groups were talking about what to have for lunch, or about football, or whatever, they could go on for hours. Once it came around to work-related topics, though, the conversation slowed down to a crawl while the HKers tried to grok the mainland-style technical terms. Us foreigners always made fun of them for being unable to understand their own mother tongue.

I'm told an analogous situation exists among Hindi & Urdu speakers? Basic conversation is fine, but when you get into highly academic topics, one group apparently starts using Perso-Arabic words and the other group starts using Sanskrit words and communication all goes pear-shaped.

The key thing I got from this article: in French, a buffer overflow is called un dépassement de tampon. I plan to use this expression during my next code review.

Phony.

Even francophone programmers switch to English among themselves in technical speech; perhaps subconsciously, call it technical diglossia if you want.

You wanna appear sophisticated? s/french/mathematics/, but learn it well and back your words up with knowledge, not parroting technical lingo and hoping no one notices you're full of it.

  There are no French programming languages, not even Pascal 
  or Eiffel uses French words for the syntax, and all the 
  documentation is in English.

Learn to speak Indian since it appears that most sophisticated programmers are from India. :) By the way, i am not from India.