In r36253 [1] I made some changes to the $linkTrail. Primarily I changed the use of a-z to use \p{L&} instead. From [2] \p{L&} is the Unicode class for [[:alpha:]] in other words, all alphabetical characters. This has fixed it so that link trails use all valid characters. As you'll see in [3] all the characters in Wikipedia's EditTools and a few more are now considered part of the linkTrail (Before 99% of those would not be part of the link)
But in addition to that I fixed an old complaint that things like [[Bar]]'s do not consider the 's as part of the link. (Don't worry, I made sure that things like ''[[Foo]]'' and '[[Foo]]' do not break)
TimStarling pointed out that some other languages have their own punctuation characters. I need some translator help compiling a list of foreign language punctuation characters used similarly to ' which should become part of the link when they come immediately after the closing ]]. I can't compile a list like this myself because I can't identify what foreign languages do with certain punctuation characters.
When that list is created, we can add it to a [] inside of the default $linkTrail. That way punctuation should be linked correctly for all languages no matter what locale is used. As TimStarling pointed out, any "ambiguity that can only be resolved ... at the language [level]" we can fix in individual languages. But for the most part, things should work for any language no matter what the current local is. After all, there's nothing wrong with having Japanese text in an English wiki, we do it all over Wikia and the Anime and Manga WikiProject on Wikipedia.
[1] http://svn.wikimedia.org/viewvc/mediawiki?view=rev&revision=36253 [2] http://www.regular-expressions.info/posixbrackets.html#class [3] http://dev.wiki-tools.com/purge/Link_Codes