Anthere-
No - we are one project at one website. It was a mistake to internationalize based on subdomains because it incorrectly gives the impression that we are on different websites. A much better system is to have internationalization based on folders; http://wikipedia.org/en/ = English version, http://wikipedia.org/de/ = German version, ect.
Could the textbook site be made international then please ?
Making a site like Wiktionary or textbook.wiki international is a lot of work with the current setup. A copy of the code and a new database has to be created for each language, and the relevant texts have to be adapted. It is better to wait a bit, but keep internationalization in mind from the start. The "textbook"-wiki will likely be relocated to wikibooks.org, where we can then use the scheme that Mav proposes.
Regards,
Erik