Thank you SOAS library - I finally got a copy of Il dialetto berbero di Sokna! Sokna (they even have a Facebook group) is a small oasis south of Sirt in Libya, whose dialect of Berber, along with that of nearby El-Fogaha, is Siwi's closest relative. There were several surprises inside, including unusual vocabulary like amerru "mountain" or imeγri "Dhuhr (the midday prayer)", and some striking features shared with Siwi; one of the main ones is an unexpected bit of allomorphy. Across Berber, the second person plural ("you guys") is expressed on the verb with t-...-m, except in the imperative; Sokna does the same, so for example "you have" is t-la-m. In the imperative, you have a suffix -t; Sokna again does the same, eg sag-it-ten iyi-leḥbes "(you guys,) take them to prison!" But if you add an indirect object pronoun ("to him" etc.) to the imperative, you replace this t with an m, like the m in the second half of the non-imperative forms: eḍbeḥ-im-as a-na-dd y-used "(you guys) tell him to come to us!" The same thing happens in Siwi, except that in Siwi the prefixed t- of the non-imperative forms has disappeared. I'm doing a paper on the development of indirect object agreement in Siwi for the Berberologie conference in July, and this is a useful pointer to its history. Amazigh readers - have you come across anything like this?
Sadly, Berber is probably no longer spoken in Sokna. When this article was written in 1911, the shaykh of the oasis reported that only 4 or 5 Isuknan could still speak it, although many more could understand a bit. I don't know whether the people of Sokna today regret the loss of their language or are glad of it - but its disappearance destroys a key not just to Sokna's history but to that of Libya, Egypt, and the whole of North Africa, leaving only this article's fairly short wordlist (and a few even shorter older sources) as evidence for migrations between central Libya and Siwa and early contact with vanished pre-Sulaymi Arabic dialects.