The statement The English (en) version of the spelling checker is used by default is actually incorrect. This rule will only fire if an assembly is marked with the NeutralResourcesLanguageAttribute or AssemblyCultureAttribute (normally for use by satellite assemblies only).
For example, specifying the following will cause Code Analysis to spell check resources using the English (United States) lexicon:
[C#]
[assembly: NeutralResourcesLanguage("en-US")]
[Visual Basic]
<Assembly: NeutralResourcesLanguage("en-US")>
[C++]
[assembly: NeutralResourcesLanguage("en-US")];
Whereas, specifying the following will cause Code Analysis to spell check resources using the English (Australia) lexicon:
[C#]
[assembly: NeutralResourcesLanguage("en-AU")]
[Visual Basic]
<Assembly: NeutralResourcesLanguage("en-AU")>
[C++]
[assembly: NeutralResourcesLanguage("en-AU")];