It seems to me that the l of baile is never pronounced as a slender consonant by native speakers. In hindsight, I can only confidently say I've ever heard it pronounced as slender by L2 speakers; teachers and students during my schooldays mostly. But, then, I don't know of any dialect in which it is spelled so as to reflect that it's a broad consonant, and I don't know of it ever being spelled with a with a double consonant, baille, in Old Irish sources.

Any ideas how the pronunciation came to be what it is, despite the spelling? Or is it spelled differently anywhere, and I just don't know about it?

I think what you're referring to is the 4 L's in some Irish dialects: tense broad L, lax broad L, tense slender L and lax slender L - L, l, L' and l'.

You're right that learners tend to give it an exaggerated L', which is not right, or they put an exaggerated English "y" after the l.

Cork Irish doesn't have a 4-way distinction, only lax broad l and lax slender l, and the lax slender may be closer to an English l than the L' in some words in Ulster Irish would be. Fuaimeanna (http://fuaimeanna.ie/ga/Recordings.aspx?Ortho=baile) shows this word has the lax slender l in Munster -and yet - and i was surprised to see it - shows a broad l in Ulster and Connaught (and yet the Connaught recording sounds slender).

Go fóill (http://fuaimeanna.ie/ga/Recordings.aspx ... f%C3%B3ill) shows the difference between tense and lax slender l, but I admit I can hardly hear anything.

Irish lax slender l´ is like the "normal" and often only l sound in many languages.

A learner would probably expect some kind of extra palatalisation features or so because it is "made slender", but no, it is just a simple /l/.
On the other hand, learners could probably expect broad Irish l to be the "normal" variant, but no, broad l (lax and tense) is heavily velarised: /ɫ/ and /ɫ̪/

Haigh

The "l" is single slender in "baile" in all Irish dialects (while non-native speakers mostly pronounced "balyeh" because they don't know how to pronounce a single slender L...).

"Go fóill" isn't a good example of slender LL because it's an exception, it's pronounced as if spelt "go fóil" in Donegal.
There are examples of slender LL in the words leaba and leabhar.

I don't agree with some of the transcriptions of that website... (Also they write phonetics between slashes... wtf, only phonology should be written between slashes, phonetics should be written between square brackets).

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Is fearr Gaeilg na Gaeltaċta ná Gaeilg ar biṫ eile
Agus is í Gaeilg Ġaoṫ Doḃair is binne

Thank you. So l at the start of a word is always LL in Ulster. leaba is in the database at http://fuaimeanna.ie/ga/Recordings.aspx?Ortho=leaba

As Labhrás states, the Engish light l is like a slender single l in Irish. Of course, although palatalisation and velarisation are not phonemic in English, that doesn't mean we don't have consonants that are typically "slender" - l, n in most positions and k and g and ng. And the English alveolar t and d are closer to being slender than broad.

The English word "lull" starts with a slender l and ends with a broad l (but the broad l can be vocalised into a w).

For Munster Irish usually baile has a slender l.

As for slender l itself, in Munster it's basically just the English l, [l], next to front vowels like in líon, but it's [lj] next to back vowels like in oileán.

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The dialect I use is Cork Irish.
Ar sgáth a chéile a mhairid na daoine, lag agus láidir, uasal is íseal

Unlenited (or eclipsed) initial L's are double indeed :
lá is pronounced like llá
leabaidh is pronounced like lleabaidh

Now, in traditional speech (older speakers, not so sure concerning younger speakers, even speakers under 60 actually, I think they make much fewer differences, there are much fewer phonemes), lenited l's become single, so "mo leabaidh" has a single slender L : roughly "leabaidh" alone is "lyah-bwee", but "mo leabaidh" is "maw lah-bwee" (I think not-old speakers would say "maw lyah-bwee" though).


"ó lá" has a single broad L.
Normally, when you say "ó lá go lá", the 2 L's sound different.

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Is fearr Gaeilg na Gaeltaċta ná Gaeilg ar biṫ eile
Agus is í Gaeilg Ġaoṫ Doḃair is binne

Here's a curiosity. Word-final 'ch' is generally silent in Ulster Irish. Therefore, you would expect that 'baile' and 'baileach' would be pronounced identically. But it turns out that this is not so, per the recordings in teanglann.ie - the difference being the l sound.

Baile (https://www.teanglann.ie/ga/fuaim/baile): Ulster Irish has a plain l here (i.e. an l that is neither palatised nor velarised) i.e. same as English light l.

Baileach (https://www.teanglann.ie/ga/fuaim/baileach): Ulster Irish clearly has a palatised l here.