I've spent the past couple of days at the Berberologie colloquium in Leiden, and it's been great fun. There were plenty of very interesting speakers, but for me two languages stole the show: Tetserrét and Ghomara.
Tetserrét (discussed by Cécile Lux) is spoken by a Tuareg tribe, the Ayt-Tawari, in Niger. But it's not linguistically Tuareg at all - its closest relative is Zenaga, the Berber of Mauritania (not northern Berber, contrary to Wikipedia), and Tuaregs can't even understand it. It seems to be an isolated survival of the Berber language spoken in the region before the Tuareg got there. It's not in Ethnologue either. (Taine-Cheikh's new Zenaga dictionary is out, by the way, and was selling as fast as a book reasonably can in a conference of twenty people.)
But Ghomara, in northern Morocco, is something else. Across Berber, borrowed Arabic nouns typically behave like in Arabic (keeping their Arabic plurals, and not changing for case.) In Ghomara (discussed by Jamal El Hannouche), Arabic adjectives take Arabic rather than Berber agreement marking - and even some Arabic verbs get conjugated fully in Arabic, not in chance code-switching but regularly by all speakers, and up to and including pronominal object suffixes. It's not quite unprecedented worldwide, but that level of contact influence is pretty darn rare.
I didn't put Tadaksahak in the first paragraph because it's much less unfamiliar to me, but Regula Christiansen's paper on that had some interesting implications. Basically, Tadaksahak has all but lost the Songhay method of forming attributive adjectives; instead, it's substituted a simplified version of the Tuareg one (suffixing -an), which has become productive for Songhay adjectives too. The funny part is this: Songhay has a lot of CVC adjectives (stative verbs). Tuareg doesn't really do CVC adjectives; it prefers longer words. So when you add the -an to these, you typically reduplicate the adjective. For example, kan "be sweet" > kankanan "sweet". This comes worryingly close to invalidating a conjecture I had made on the borrowability of templatic morphology (but not quite!)
My own paper established that much of the Berber element of Kwarandzyey derives from an extinct close relative of Zenaga. In effect, the "Western Berber" genetic subgroup of Berber has four members: Zenaga itself (finally with a decent dictionary), Tetserrét (awaiting further publications), the large Berber element of Hassaniya, and part of the proportionally larger Berber element of Kwarandzyey.