We have been trying pretty much all solutions posted above for the past couple months. I also appreciate your attempt to fix SquareSpace with your script but this is not a good solution for us :)
Our last hope was to use LocalizeJS which seemed very promising (even though it gets quickly quite expensive). After a couple days we had our website in two languages. Defaults to french, option to switch to english.
But here is the trick: when using LocalizeJS the pages in each language have the same URL. This is just unacceptable for SEO. Google is simply not able to see our website in english, which is dramatic since almost 30% of our revenue comes from english-speaking countries. And even if Google was able to find and run the JavaScript provided by LocalizeJS, it could not attach a unique URL for a given language.
I reached out to LocalizeJS support and they suggested that we tweaked their loading script to detect either a subdirectory (mycompany.com/en) or a subdomain (en.mycompany.com) and load the appropriate language. Since the subdirectories solution does not work with SquareSpace (the menu is built automatically) I tried to configure a subdomain.
But here again there is catch: SquareSpace will redirect any subdomain (or alternative domain) to the main domain name. Therefore en.mycompany.com redirects immediately to www.mycompany.com.
Conclusion: we have decided for now to create a second website, in english this time, until SquareSpace adds support for localization... or until another high-quality website builder supports localization.
I hope my investigation can save you some time :)
