The xml:lang attribute is an XML-defined attribute that declares the language and culture information for an element in XML. This same meaning of the attribute persists in XAML; however, some additional considerations apply.
<object xml:lang="rfc3066lang" />
The definition for the xml:lang attribute in XAML is derived from xml:lang as defined as a "special attribute" by the World Wide Web Consortium (W3C) for XML. Language and culture information is potentially processed in different ways by elements, depending on their implementations; however, there is no default XAML processing of the xml:lang attribute.
The default value of the xml:lang attribute is an empty string at the attribute level.
The xml:lang attribute effects and the value of the attribute are generally perpetuated to child elements, when interpreted by systems that act on xml:lang values.
When interpreted by XAML writers of .NET Framework XAML Services, an xml:lang value can create XmlLanguage or CultureInfo objects in the underlying object representation; however, that behavior depends on whether the value specified for xml:lang is a valid construction for those classes.
Frameworks can create associations between framework-defined properties and the meaning of xml:lang in XML by applying XmlLangPropertyAttribute to the property.
For elements that are derived classes of FrameworkElement or FrameworkContentElement, you can use the equivalent dependency property instead of the xml:lang attribute. By default, the property uses "en-US" if it is not otherwise set, either through the property or through processing the xml:lang attribute.