The extremaduran language which I refer to is the "high extremaduran" (probably spoken by some tens of thousands), the one considered to be the language, derived from the historical asturleonese dialect of latin (just as the portuguese derive from the galician-portuguese historical latin dialect, or the spanish from the castilian historical latin dialect). The ethnologue mixes this high extremaduran, the language, with the "middle" and "low" extremaduran, already (and since centuries) castilian dialects.
What I said is that the castilian dialect of Extremadura is similar -logically- to the extremaduran language, as the english from Cornwall is similar to the cornish language - both share vocabulary and some verbal and phonological features; much more in this case where extremaduran and the language which absorved it in those territories (spanish) are from the same linguistic family.
The fala (or galaico-extremaduran) is a galician-portuguese language, like the galician and portuguese (and by no means a portuguese or galician dialect such as brazilian), so similar to spanish as the portuguese or the galician (both with its own wikipedia). The extremaduran language is so intelligible with spanish as the asturian language or the aragonese (both with its own wikipedia too).
Every romanic linguistic variety is more or less intelligible to each other, but there are degrees of comprehension, and one old high extremaduran without having learned spanish at school has no more comprehension of spanish than a norwegian understands swedish, or more than a mother-tongue galician understands spanish (of course they can understand the languages of the same family, and they usually do, but they always loose information).
The reason why I said that more than 1.500.000 could use the extremaduran language is to show the number of people who could be interested in using it, the people who -like me- speak the castilian-extremaduran dialect in the provinces of Salamanca, Cáceres, Badajoz and Huelva (counting with the emigrated probably near 2.500.000 people).Just as one basque would be interested in using the basque wikipedia, even if he doesn't really speak the basque language, only because in the castilian that he speaks remains features of the old regional language, and because of 'regional love', so to say, to defend the "own" historical language.
But of course I am talking about languages, which by definition are not mutually intelligible (at least to a good degree). I would never propose to make a wikipedia in dialectal spanish from Extremadura, or dialectal spanish from Andalusia or from Murcia, or from the american spanish (argentinian, mexican,...). That would be an aberration, I have always struggled with people not to propose such kind of desintegration of the spanish domain: I speak spanish. Extremaduran spanish. But not extremaduran. Extremaduran is a language derived from latin (through the old astur-leonese dialect). I wouldn't accept ever something like creating the "argentinian language" only because the argentinians may feel they speak a different spanish, to present an example. And so wouldn't I with extremaduran spanish. You have in me a defender of the integration of dialects into standardized languages (so with the extremaduran language). But of course not of absortion of the minority languages by the official and important ones.
Anyway, apart from this, I also believe that languages should be used to communicate with the more people possible, that is why I learned english. But the fact that the Wikipedia is written in a lot of regional minority languages of western Europe (where almost everyone learn at school their country's official language, and many also english) reveals that Wikimedia also defends the regional languages, because of its intrinsecal cultural value and because of the attraction that causes in its speakers (and the groups who spoke it in the past, like in the case of the cornish or basques), speakers who other way would maybe never read the wikipedia (if it were only in english or spanish, for example). You have the example of the catalan wikipedia, which as far as I know receives lots of articles - and only a few catalan-speakers cannot communicate in spanish, and I don't think theese ones use the wikipedia or even the internet...-. So there are a lot of people who understands spanish and catalan more willing to use their regional language than the spanish, that is obvious.
So: castilian/spanish of Extremadura (dialectal spanish, or dialectal english,...) NO. But extremaduran, why not? No doubt there is a line to be drawn between wikipedia factible languages and not factible ones - we could say: "we will not start any wikipedias in artificial languages", or "we will not start wikipedias in death languages", or even "neither of them, but for the ones actually used" (like the artificial esperanto or the death cornish, both widely accepted today as present languages). But who could so easily say that the last two languages of Spain without wikipedia (the others have it already) don't deserve having it? And, most important, why? Who could say: this tongue is too similar to spanish, while portuguese, asturian or spanish aren't?
Sorry for the big mail. Be what it be the final decision, I needed to explain to all those who have interest about the spanish language domain the difference between the spanish of Extremadura and the extremaduran language, almost everywhere in the net confused and mixed altogether (probably because they share the same name: "extremaduran").
By the way, the region of Extremadura is following a programme of massive computer acquisition for public institutions (as a consequence of the money saved in software, due to the use of Linex, a kind of 'Linux from Extremadura'), what makes more and more accessible the internet to those old high extremadurans from little towns who speak the language and have a lot of time to use the www.
[For more information on the extremaduran language actual domain you can visit http://en.wikipedia.org/wiki/Spain#Languages ; for still more information on the extremaduran language and the extremaduran spanish dialect you can visit http://es.wikipedia.org/wiki/Extreme%C3%B1o , where it is clearly distinguished between both - the high extremaduran and the rest. The Spanish Linguistic Organization Proel.org also has a good map and some information at http://www.proel.org/lenguas.html . The ethnologue information obviously mixes information about the extremaduran language and the extremaduran spanish dialects, with a map of the administrative region of Extremadura, and not actually its territory]