East Asia, Africa and most of the old USSR. For ATC it may be but not for actual air travelers.

was on a QF from SYD to HKG and announcements were done in English, Cantonese and Mandarin. The cantonese and mandarin was done pretty badly though, lots of mumbling. Domestic flights to shanghai would use Wu chinese instead of cantonese i think?

in china they sure as hell don't use a whole lotta english...where i am now (zhuzhou, hunan) english is non existent and you'd struggle to do anything with english

YMMV. On my Shandong Airlines flight from Lanzhou to Urumqi in June, English (but no Uyghur) was used for announcements too. Possibly for the only gringo (me) aboard? Heh...luckily, I don't really need it, but regarding that flight, another issue arose. The flight was delayed about 3-4 hours, and no announcements were made at Lanzhou Airport, let alone in English. Surprisingly, SC provided both a (decent) meal and a room at the airport hotel, but without being aggressive/knowing the lingo, how would the others know?

In case you're curious, the day I took that flight was the day a Nordwind jet from Phuket to somewhere in Siberia emergency landed in Lanzhou.

I agree with this: sometimes the announcements are so garbled that I cannot understand even the ones in a language I understand well. Occasionally one just has to hope that they're telling the passengers something routine rather than something of an urgent nature...

Doesn't depend on the point of departure and the point of arrival, and the nationality of the airline. For example, on an Air France flight from Paris to Casablanca, I'd be surprised if the lingua franca would be considered to be English, although announcements might be made in English.

I think perhaps in places like China, where everyone is essentially expected to understand Mandarin to some degree (although to what degree and the ability to speak is a different matter) that this is somewhat less of an issue. Of course there may be the odd person here an there without the ability to understand Mandarin, but with the education system based in Mandarin, I would expect the occurrence of such passengers being extremely low.

I recently caught an Air Canada flight (LAX-YVR) with my French speaking mother.As expected, there were announcements in both English and French (the FAs were both French speaking) but my mother could barely understand the French announcement due to the thick accent and difference in vocabulary and even some grammar! :D

I put this down to both my mother and the FAs speaking different non-Metroplitan French

actually now that i think of the the most annoying announcements in multiple languages is the automated ones in the HK MTR, in english, cantonese, mandarin, automatically played on arrival at every station, often enough for it to be considered brainwashing i think....

I think I've heard 5 languages on NRT-BKK flight a while back.
English, Japanese, Thai, Mandarin and Cantonese.
It's too much. At the maximum, there should use 3 languages; origin language, destination language, and the language of the country that the operating carrier is registered to.

But what if (as per examples above) the origin and destination are multilingual (and perhaps have laws about the use of language), and you're expecting a large proportion of transfer passengers from all over?

In Singapore, Mandarin is the official language, dialects are not recognised and so not used. So on the subway/MRT, yes - in all 4 languages. But on SQ, only English and language of origin/destination/stopover.

i would love to see AirNZ start doing announcements in Maori......

I've only encountered announcements in Maori once - on an Emirates flight ironically. Needless to say, it went down a treat with the NZ (of all ethnicities) passengers. I'd dare say that the other passengers who hadn't traveled to NZ before must have assumed this was standard practice

Thinking about it, it could be quite a political minefield. I seem to remember Aer Lingus came under fire for dropping Irish on ex-Belfast flights, and I know I've had flights to/from Switzerland that have featured announcements in what I can only assume is Romansch.

But otherwise what do flights to/from Spain do - always in Castilian, or also in Catalan, Basque, Gallician, Valencian..? Flights from Brussels always use French and Dutch, but would flights from Antwerp do the same? But then how far do you take it? Do you hear Frisian, Scots Gaelic, Swabian, Nynorsk, Jysk, Elsässerditsch, Breton, Welsh..?

ZRH-GVA (on LX) routinely has 4 languages (English, French, German, Italian).

Don't know if I'd describe Spain and France as "the extreme parts of nowhere" myself, but each to their own (linguistic ignorance.)

Funny enough, if there's one place in the world where you can't expect to get by in day-to-day life using your native language it's parts of the Middle East. In particular those places with holes dug in them to let black gooey stuff out. You simply won't find a local working in a shop or restaurant or any other "menial" job anywhere in Dubai, Kuwait or Qatar. You might be lucky in Saudi, Oman or Bahrain to catch a local driving your taxi, but the bloke or sheila behind the counter will always be someone from the sub-continent, and the other sheila serving your beer or bringing your food will be from further East; Phlips, Thai or Indon. Thus, while the official language might be Arabic, the language by far most used and spoken is English. Usually with a Jinglish touch to it. Funny old world.