Just back from a nice evening with the Siwi community of Qatar. A Kabyle friend came along (hello if you're reading this!), giving me a chance to see first-hand to what extent Siwi and Kabyle are mutually comprehensible. The answer is: very little indeed. Looking through basic vocabulary it's not hard to find cognates; but when it comes to even short sentences, mystified expressions on both sides were the order of the day. The Berber languages of Algeria and Morocco may shade into one another to some extent, even across sub-family boundaries - there seem to be dialects for which it is difficult to decide whether they should be called Kabyle or Chaoui, for example. But by the time you get to Siwa, it's quite clear that you're dealing with a different language, even by Arabic speakers' rather generous standards. Further confirmation, if any was needed, that Berber is a language family, not a language.