In which dialects have the sounds "ゐ" (wi) and "ゑ" (we) been preserved, and are their kana still occasionally seen?

In Nate Glenn's answer to bdonlan's qestion "Why were ゐ and ゑ eliminated?" he states:

"Wi" and "we" are still in some dialects, but standard Japanese does not have those sounds.

My question is which dialects are they which preserve these sounds? Plus I wonder if these dialects are on occasion still written with these obsolete kana?

Answer

It really all depends on how you define preservation, and whether you consider the Ryukyuan languages (such as Okinawan) separate languages or dialects of Japanese, since ゑ and ゐ are used in some Ryukyuan spelling systems (other systems use other conventions such as writing these sounds as うぇ and うぃ). There are one or two problems with considering that as a preservation of the historical ゑ and ゐ:

1. 
   

   While most Japanese would count Okinawan as a dialect of Japanese (though it's usually officially called 沖縄方言, Okinawan regional speech, and not 沖縄弁), most linguists tend to view it as an entirely different language related to Japanese, just like English and German are related. For what it's worth, Okinawan and Japanese are completely and utterly mutually unintelligible. So far that it's probably easier for an Italian to understand French than for a Japanese speaker to understand Okinawan.

   
   



2. 
   

   I'm not very good on the history of Ryukyuan languages, and I don't have reference material about them, so I'm not entirely sure that what's written today as ゑ and ゐ actually derives from the original sounds those letters represented in Old Japanese, or whether it is a reflex of completely different sounds.