diff --git a/languages/ConverterRule.php b/languages/ConverterRule.php
index dc61519c692..6ce1274be3a 100644
--- a/languages/ConverterRule.php
+++ b/languages/ConverterRule.php
@@ -153,25 +153,27 @@ class ConverterRule {
 			$to = trim( $v[1] );
 			$v = trim( $v[0] );
 			$u = explode( '=>', $v, 2 );
+			$vv = $this->mConverter->validateVariant( $v );
 			// if $to is empty (which is also used as $from in bidtable),
 			// strtr() could return a wrong result.
-			if ( count( $u ) == 1 && $to !== '' && in_array( $v, $variants ) ) {
-				$bidtable[$v] = $to;
+			if ( count( $u ) == 1 && $to !== '' && $vv ) {
+				$bidtable[$vv] = $to;
 			} elseif ( count( $u ) == 2 ) {
 				$from = trim( $u[0] );
 				$v = trim( $u[1] );
+				$vv = $this->mConverter->validateVariant( $v );
 				// if $from is empty, strtr() could return a wrong result.
-				if ( array_key_exists( $v, $unidtable )
-					&& !is_array( $unidtable[$v] )
+				if ( array_key_exists( $vv, $unidtable )
+					&& !is_array( $unidtable[$vv] )
 					&& $from !== ''
-					&& in_array( $v, $variants ) ) {
-					$unidtable[$v] = [ $from => $to ];
-				} elseif ( $from !== '' && in_array( $v, $variants ) ) {
-					$unidtable[$v][$from] = $to;
+					&& $vv ) {
+					$unidtable[$vv] = [ $from => $to ];
+				} elseif ( $from !== '' && $vv ) {
+					$unidtable[$vv][$from] = $to;
 				}
 			}
 			// syntax error, pass
-			if ( !isset( $this->mConverter->mVariantNames[$v] ) ) {
+			if ( !isset( $this->mConverter->mVariantNames[$vv] ) ) {
 				$bidtable = [];
 				$unidtable = [];
 				break;
diff --git a/languages/LanguageConverter.php b/languages/LanguageConverter.php
index ea26c64dc7a..137fe87d1e8 100644
--- a/languages/LanguageConverter.php
+++ b/languages/LanguageConverter.php
@@ -1175,8 +1175,21 @@ class LanguageConverter {
 			//    [1] => 'zh-hant:<span style="font-size:120%;">yyy</span>'
 			//    [2] => ''
 			//  ]
-			$pat = '/;\s*(?=';
+			$expandedVariants = [];
 			foreach ( $this->mVariants as $variant ) {
+				$expandedVariants[ $variant ] = 1;
+				// Accept standard BCP 47 names for variants as well.
+				$expandedVariants[ LanguageCode::bcp47( $variant ) ] = 1;
+			}
+			// Accept old deprecated names for variants
+			foreach ( LanguageCode::getDeprecatedCodeMapping() as $old => $new ) {
+				if ( isset( $expandedVariants[ $new ] ) ) {
+					$expandedVariants[ $old ] = 1;
+				}
+			}
+
+			$pat = '/;\s*(?=';
+			foreach ( $expandedVariants as $variant => $ignore ) {
 				// zh-hans:xxx;zh-hant:yyy
 				$pat .= $variant . '\s*:|';
 				// xxx=>zh-hans:yyy; xxx=>zh-hant:zzz
diff --git a/tests/parser/parserTests.txt b/tests/parser/parserTests.txt
index bbd9ecbe990..50c6a891b94 100644
--- a/tests/parser/parserTests.txt
+++ b/tests/parser/parserTests.txt
@@ -22434,6 +22434,19 @@ language=zh variant=zh-tw
 <p><span typeof="mw:LanguageVariant" data-parsoid='{"tSp":[6]}' data-mw-variant='{"twoway":[{"l":"zh","t":"China"},{"l":"zh-tw","t":"Taiwan"}]}'></span>, not China</p>
 !! end
 
+!! test
+Explicit definition of language variant alternatives (BCP 47 codes)
+!! options
+language=zh variant=zh-tw
+!! wikitext
+-{zh:China;zh-Hant-TW:Taiwan}-, not China
+!! html/php
+<p>Taiwan, not China
+</p>
+!! html/parsoid
+<p><span typeof="mw:LanguageVariant" data-parsoid='{"tSp":[6]}' data-mw-variant='{"twoway":[{"l":"zh","t":"China"},{"l":"zh-Hant-TW","t":"Taiwan"}]}'></span>, not China</p>
+!! end
+
 !! test
 Filter syntax for language variants
 !! options