参见 MSDN包清单的内容 部分 > 资源

默认情况下它只会包含

<Resource Language="x-generate"/></资源>

在构建清单时，源清单文件 (package.appxmanifest) 中使用的资源语言标记x-generate"将替换为实际语言代码.

所以基本上，在使用 GUI 编辑清单时，清单中的默认语言是任何语言.

如果您想添加更多语言，只需添加另一个Resource

<Resource Language="x-generate"/><Resource Language="en-us"/><Resource Language="en-gb"/></资源>

Its easy to add multiple language support in Windows Phone 8.0 WMAppmanifest file, as it have a list of all languages to select from.....
But I dont find any field in 8.1 WMAppmanifest file to add support for multiple language because during app submission on store it says only English supported which is default language. I have added strings resources for different languages but need to find a way to add another language.

See MSDN Contents of the package manifest Section > Resources

By default it will only contain

<Resources>    
    <Resource Language="x-generate" />
</Resources>

The Resource Language token "x-generate" that's used in the source manifest file (package.appxmanifest) is replaced with the actual language code when the manifest is built.

So basically whatever language is the default language in in the manifest when editing it with the GUI.

If you want to add more languages then just add in another Resource

<Resources>    
    <Resource Language="x-generate" />
    <Resource Language="en-us"/>
    <Resource Language="en-gb"/>
</Resources>