Unless you've been stuck on an iceberg in the Antarctic, you probably know that the Tunisian people have earned themselves imperishable honour, no matter what happens next, by kicking out their thieving, torturing control freak of an ex-president Ben Ali. Mark Liberman (via LH) has already commented on his unusual choice of dialect in his last speech. Fortunately, he's yesterday's news, so I'm going to comment instead on the language being used by the newly significant figures jockeying for power. Due warning: the sociolinguistics of politics is not my specialty, and I don't have much prior experience of specifically Tunisian language use, so read on at your peril and feel free to correct me if you have a better idea. For non-Arabic speakers, the key point to remember is that in any one country Arabic has at least two basic levels - formal Fusha and dialectal Darja - which are different enough grammatically and lexically to be considered separate languages, but which can be combined in appropriate circumstances.
The Prime Minister is Mohamed Ghannouchi. He first came to prominence on Saturday when he briefly declared himself acting President. This speech was entirely in Fusha - no efforts to add a personal touch here, simply officialese. The only dialectal features I notice are the pronunciation of jīm as ž, and of some short low vowels as ə. The delivery, however, is notably non-fluent - he's reading it slowly from a paper, pausing sometimes every three or four words, and he makes a mistake in case marking ('ad`ū kāffati 'abnā'i tūnəs "I call upon all the sons of Tunisia" - should have been kāffata.) Today, as Prime Minister he announced the new cabinet; his speech is a bit less halting (although still halting enough that you get several elision failures, like li al-ħayāti l`āmmah for lilħayāti l`āmmah), but as before it is entirely in Fusha and is being read out from a paper. The names, however, are pronounced in Darja, as they would be in conversation. Reminiscent of Chadli Bendjedid, this looks like the delivery of a politician who feels the need to speak Fusha for symbolic reasons but isn't actually fluent enough in it to do so impromptu - he was born in 1941, when Tunisia's educational system still operated largely in French. More tellingly, his delivery betrays the fact that he has never had the need to master rhetoric or appeal to a mass audience.
Moncef Marzouki, a secular leftist opposition figure calling for the old ruling party to get out, similarly sticks to Fusha throughout a recent interview with Aljazeera, avoiding dialect forms with remarkable persistence. His language use nonetheless contrasts strikingly with Mr. Ghannouchi's: Mr. Marzouki speaks quickly and fluently off the cuff, without consulting any visible notes, and without any conspicuous errors in delivery. Yet Mr. Marzouki is only 4 years younger than Mr. Ghannouchi, and, having studied medicine, undoubtedly did his university in French; has he simply been more motivated to learn to speak to a wide audience? The choice of consistent Fusha seems to reflect Aljazeera's pan-Arab audience; in an older video, aimed more at a Tunisian audience, he again speaks primarily in Fusha, but makes a number of shifts into Darja, for example evoking immediate reactions (eg, with Darja underlined: lākin anā lammā wužəht bihād əṭṭalab qult: āš nənžəm nḍīf 'anā? "But me, when I was faced with this request, I thought: "What can I add?") or quoting proverbs (eg sāl əlmužaṛṛab ma tsālš əṭṭbīb "Ask a person with experience, not a doctor") The effect, to me, is reminiscent of a classroom lecture.
The regime's favourite bogeyman for many years, the Islamist leader Rachid El Ghannouchi, has announced plans to return shortly, though not to run for office. In his speech of 2 days ago, he uses Fusha consistently and fluently, with an intonation reminiscent of a sermon, and shows only sporadic dialectal phonetic features (eg qámə` for qam` "repression"). Yet he shifts into Darja briefly (at about 4:50): after warning security forces that those who kill innocents will be damned to Hell, in the maximally formal language of a quotation from the Qur'an (wa-may͂ yaqtul mu'minan muta`ammidan, fa-žazā'uhu žahannamu xālidan fīhā, wa-ġaḍiba ḷḷāhu `alayhi wa-la`anahu wa-'a`adda lahu `ađāban 'alīmā "Whoso slayeth a believer of set purpose, his reward is hell for ever. Allah is wroth against him and He hath cursed him and prepared for him an awful doom"*), he suddenly caps it with a brief colloquial appeal to their common sense: əṭṭāġiya muš məš isədd a`līk "the tyrant isn't gonna save you". I can't hear any obvious traces of his southern origin (no g replacing q, for example), but I don't know Tunisian dialects well enough to spot subtler indications.
As for the protesters? Well, listen for yourself to one of the latest. Some slogans are definitely dialectal: Tūnəs, Tūnəs, ħəṛṛa ħəṛṛa, wa-t-tažammu` `ala baṛṛa "Tunisia free, RCD out!" Others are purely Fusha (though minus inconvenient case endings, as is common in less formal Fusha): yā tažammu` yā žabān, ša`b tūnəs lā yuhān "RCD you cowards: The people of Tunisia will not be belittled!"** Not hearing anything in French though, which is interesting given its prominent position in the Tunisian sociolinguistic environment: I suspect French would (rightly) be viewed as inappropriate for an appeal to the people of the nation, no matter how many people may speak it as a second language, whereas Fusha or Darja are equally suitable for demonstrations.
*: Stupid mistake corrected, and Pickthal translation of 4:93 substituted. It was getting late when I wrote that.
**: Looks like I misheard this one too! Corrected following Bilel's comments below. I guess transcribing YouTube videos is a risky business.