If the source document does not specify what language it is written in using the lang or xml:lang attribute. then it is assumed to be in the language this parameter is set to. If these attributes are present (and in effect, whenever the stylesheet needs language information), the language specified in this parameter is ignored.

You rarely need to change this parameter; it is better to change the source document instead, adding the lang or the xml:lang attribute.

The format of the value of this parameter is the usual language_code-country_code. For example, zh-TW. The hyphen (-) may also be an underscore (_).