Check the MediaWiki:Disambiguationspage language message - it exists for all languages. It lists all the templates that mark Disambig pages.
(https://fr.wikipedia.org/wiki/MediaWiki:Disambiguationspage for the french wikipedia, https://en.wikipedia.org/wiki/MediaWiki:Disambiguationspage for english). I'm sure there are easy ways to check if a page is Disambig in PHP - not sure about JS.