Use correct BCP 47 language codes in lang="…" attributes

A small mistake made in I7a82143. This is only relevant for very few
(but critical) language codes. For example, the dialog allows to add
the MediaWiki code "zh-classical". This needs to be translated to
"lzh", but only when we use it directly in HTML.

Bug: T238329
Change-Id: Ifcbb877fb6a348937e85a82459e924548f5ca856

extension.json

@@ -91,6 +91,7 @@
 			],
 			"dependencies": [
 				"mediawiki.api",
+				"mediawiki.language",
 				"mediawiki.user",
 				"oojs-ui-core",
 				"oojs-ui-widgets",

modules/ext.templateDataGenerator.editTemplatePage/Dialog.js

@@ -698,7 +698,7 @@ Dialog.prototype.onLanguageDropdownWidgetSelect = function ( item ) {
 
 		// Update description value
 		this.descriptionInput.setValue( this.model.getTemplateDescription( language ) )
-			.$input.attr( { lang: language, dir: 'auto' } );
+			.$input.attr( { lang: mw.language.bcp47( language ), dir: 'auto' } );
 
 		// Update all param descriptions in the param select widget
 		this.repopulateParamSelectWidget();
@@ -1253,7 +1253,8 @@ Dialog.prototype.updateParamDetailsLanguage = function () {
 		// * templatedata-modal-table-param-type
 		var label = mw.msg( 'templatedata-modal-table-param-' + prop, this.language );
 		this.propFieldLayout[ prop ].setLabel( label );
-		this.propInputs[ prop ].$input.attr( { lang: this.language, dir: 'auto' } );
+		this.propInputs[ prop ]
+			.$input.attr( { lang: mw.language.bcp47( this.language ), dir: 'auto' } );
 	}
 };