Is there a way of setting culture for a whole application? All current threads and new threads?

In .NET 4.5, you can use the CultureInfo.DefaultThreadCurrentCulture property to change the culture of an AppDomain.

For versions prior to 4.5 you have to use reflection to manipulate the culture of an AppDomain. There is a private static field on CultureInfo (m_userDefaultCulture in .NET 2.0 mscorlib, s_userDefaultCulture in .NET 4.0 mscorlib) that controls what CurrentCulture returns if a thread has not set that property on itself.

This does not change the native thread locale and it is probably not a good idea to ship code that changes the culture this way. It may be useful for testing though.

This gets asked a lot. Basically, no there isn't, not for .NET 4.0. You have to do it manually at the start of each new thread (or ThreadPool function). You could perhaps store the culture name (or just the culture object) in a static field to save having to hit the DB, but that's about it.

If you are using resources, you can manually force it by:

Resource1.Culture = new System.Globalization.CultureInfo("fr"); 

In the resource manager, there is an auto generated code that is as follows:

/// <summary>
///   Overrides the current thread's CurrentUICulture property for all
///   resource lookups using this strongly typed resource class.
/// </summary>
[global::System.ComponentModel.EditorBrowsableAttribute(global::System.ComponentModel.EditorBrowsableState.Advanced)]
internal static global::System.Globalization.CultureInfo Culture {
    get {
        return resourceCulture;
    }
    set {
        resourceCulture = value;
    }
}

Now every time you refer to your individual string within this resource, it overrides the culture (thread or process) with the specified resourceCulture.

You can either specify language as in "fr", "de" etc. or put the language code as in 0x0409 for en-US or 0x0410 for it-IT. For a full list of language codes please refer to: Language Identifiers and Locales