You can use WultraMobileToken.setAcceptLanguage set to the user's preferred language for all WMT services.
If you're creating services manually (e.g., WMTOperations), you can set the acceptLanguage property directly.
The default value is always en. With other languages, we use values compliant with standard RFC Accept-Language.
The language properties are just a wrap-around of the underlying networking language configuration described in our networking library documentation.
Note: Content language capabilities are limited by the implementation of the server - it must support the provided language.