OpenDocument not working in Chrome (language settings problem)

This is a strange one.

I'm a Brit, living in Switzerland, so my Windows 7 regional settings is set as English, but my keyboard is Swiss German.

When I attempt to use OpenDocument from my RESTful web site, it works fine in IE11, but barely opens properly in Chrome  (see attached image).

Opening the Developer Options in Chrome, and looking at the Network tab, I can see that it's looking for files which don't exist, like this one:

http://MyServer:6405/BOE/OpenDocument/160312/AnalyticalReporting/webiDHTML/dhtmllib/language/de/labels.js

Whereas in IE, it looks for this file, which does exist:

http://MyServer:6405/BOE/OpenDocument/160312/AnalyticalReporting/webiDHTML/dhtmllib/language/en/labels.js

Also in Chrome, it attempts to find "dialogservice_strings_de.js", which also doesn't exist on our server, and a load of JavaScript errors appear (as shown in the attached image).

Can someone tell me how to tell the OpenDocument / BO Server to just use the English language ?

I've scanned through the documentation... but nothing. 

I can't see any mention of how to set the language.

Can anyone help, please ?