A class of speech sounds fairly rare in the world's languages. The most familiar languages that have them are Welsh, Zulu, Navaho, and Tibetan. Oh, and Klingon.

Most languages have laterals, which are L sounds. Almost all languages have fricatives, where the mouth is constricted enough to cause audible friction as the sound passes. But almost all laterals are frictionless: a lateral fricative is the rare combination of an L sound simultaneous with the friction of TH or SH.

My experience of classes and textbooks is that lateral fricatives are glossed over as oddities, to be mentioned but no more. Most of what I'm about to explain I had to work out for myself. As a child I played with sounds and invented languages with weird noises gleaned from wrong understanding of precocious reading of phonetics. Later after I'd studied phonetics, and these weird sounds didn't appear anywhere, it took me years of mulling over before I could reconcile them.

A book (whether on linguistics, or Teach Yourself Welsh) typically says that a lateral fricative is something like THL coarticulated. As a lateral, one side of the mouth is blocked by the tongue and the other is open enough for air to pass through; and as a fricative that air passing through is rough, like TH. The sound of L is usually made in the front of the mouth, typically a dental, and the corresponding fricative sound in that position is TH.

What I was never told was that lateral fricatives can vary in place of articulation just as fricatives can, restricted however in how far the tongue can reach. But you can definitely have THL-like dental lateral fricatives and SHL-like palatal ones. The corresponding voiced sounds are DHL-like and ZHL-like.

The Nguni languages of southern Africa, that's Xhosa and Zulu and Swazi, have dental lateral fricatives, written hl (voiceless, THL-like) and either dhl (voiced, in Zulu, as in Isandhlwana) or dl (in Swazi, as in the common surname Dlamini). I recently read - I think it was in Teach Yourself Xhosa - that these sounds were definitely dental, unlike the Welsh one.

The Lh of Tibetan Lhasa is apparently a lateral fricative, but I know no more detail on it.

Welsh ll is the most familiar of all, if you're trying to pronounce places like Llangollen and Llanelli. Now I've hardly been in Wales at all, and don't know how it varies regionally or by age. My native speakers are an expatriate community in London, and all (I think) from the same area of South Wales, but it finally clicked why what I was hearing from them wasn't what I'd been brought up to believe from books.

It's not just that Welsh uses palatal rather than dental sounds - I'd already tried that for fit and found it wanting - it's that the ll sound is not strictly a fricative but an affricate: that is it has a stop or plosive component in front of it. It is not SHLangoSHLen and SHLaneSHLi they say, it is KSHLangoKSHLen and KSHLaneKSHLi. Well, books all describe it as a fricative, so maybe this affricate pronunciation is new, or a peculiarity of that region.

And while we're at it, Klingon also has a lateral affricate, but it's dental: the TTHL sound of their self-name Tlhingan.

Lateral fricatives and affricates occur in quite a few North American languages. Some of them, notably Athapaskan languages of Canada, haven't got a plain L but have pairs of lateral affricates. These may be written in Americanist phonetic notation as either [l] (voiced) and [l] (voiceless), or as [λ] and [λ].

Nuxalk (or Bella Coola) of British Columbia is striking in that it can make almost anything syllabic, e.g. 'birthmark' is stt, three syllables: each consonant is a separate syllable! Now its lateral fricative can also be, as in nujamλ 'sing', three syllables (j = Y as in German ja). The syllabic λ is also a marker of past tense, which can be doubled up, and also of the subject pronoun 'we'. So you get the glorious hexasyllabic word nujamλλλλ 'we used to sing'.

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