es una característica de la nueva versión, después de instalar el paquete de idioma tienes que ir a Admin > Idiomas, selecciona el español, le das a "Editar" y marcas la casilla "Activar"

Muchas gracias, Ya he hecho el cambio... pero ahora tengo otro problema, Me da error el Foro, no se puede postear en el, me da un error bastante grande:

Error: is currently unavailable.
DotNetNuke.Services.Exceptions.ModuleLoadException: Object reference not set to an instance of an object. ---> System.NullReferenceException: Object reference not set to an instance of an object. at DotNetNuke.Modules.Forum.PostConnector.ProcessStripQuotes(String PostBody) at DotNetNuke.Modules.Forum.PostConnector.PostToDatabase(Int32 TabID, Config objConfig, Int32 PortalID, ForumUser objForumUser, String PostSubject, String PostBody, ForumInfo objForum, Int32 ParentPostID, Int32 PostID, Boolean IsPinned, Boolean IsClosed, Boolean ReplyNotify, Int32 ThreadStatus, String Attachment, String RemoteAddress, Int32 PollID, Int32 ThreadIconID, Int32 ParentThreadID, Boolean ProcessParseInfo, PostAction objAction) at DotNetNuke.Modules.Forum.PostConnector.SubmitPost(Int32 TabID, Config objConfig, Int32 PortalID, ForumUser objForumUser, String PostSubject, String PostBody, Int32 ForumID, Int32 ParentPostID, Int32 PostID, Boolean IsPinned, Boolean IsClosed, Boolean ReplyNotify, Int32 ThreadStatus, String Attachment, String RemoteAddress, Int32 PollID, Int32 ThreadIconID, Boolean IsQuote, Boolean ProcessParseInfo) at DotNetNuke.Modules.Forum.PostEdit.cmdSubmit_Click(Object sender, EventArgs e) --- End of inner exception stack trace ---