diff --git a/NEWS b/NEWS
index 341b29b8088..4aa580dd205 100644
--- a/NEWS
+++ b/NEWS
@@ -8,6 +8,9 @@ PHP                                                                        NEWS
 - Core:
   . Fixed bug #81380 (Observer may not be initialized properly). (krakjoe)
 
+- Intl:
+  . Update all grandfathered language tags with preferred values
+
 - OCI8:
   . Added oci8.prefetch_lob_size directive to tune LOB query performance
 
diff --git a/ext/intl/locale/locale_methods.c b/ext/intl/locale/locale_methods.c
index 159b3ea0a19..d6053b6be56 100644
--- a/ext/intl/locale/locale_methods.c
+++ b/ext/intl/locale/locale_methods.c
@@ -55,31 +55,125 @@ ZEND_EXTERN_MODULE_GLOBALS( intl )
 #define EXTLANG_KEYNAME_LEN  10
 #define PRIVATE_KEYNAME_LEN  11
 
-/* Based on IANA registry at the time of writing this code
-*
-*/
+/* Based on the IANA language subtag registry (File-Date: 2021-08-06)
+ * https://www.iana.org/assignments/language-subtag-registry
+ *
+ * This list includes all grandfathered tags, as well as redundant
+ * tags that have a Preferred-Value.
+ */
 static const char * const LOC_GRANDFATHERED[] = {
-	"art-lojban",		"i-klingon",		"i-lux",			"i-navajo",		"no-bok",		"no-nyn",
-	"cel-gaulish",		"en-GB-oed",		"i-ami",
-	"i-bnn",		"i-default",		"i-enochian",
-	"i-mingo",		"i-pwn", 		"i-tao",
-	"i-tay",		"i-tsu",		"sgn-BE-fr",
-	"sgn-BE-nl",		"sgn-CH-de", 		"zh-cmn",
- 	"zh-cmn-Hans", 		"zh-cmn-Hant",		"zh-gan" ,
-	"zh-guoyu", 		"zh-hakka", 		"zh-min",
-	"zh-min-nan", 		"zh-wuu", 		"zh-xiang",
-	"zh-yue",		NULL
+	"art-lojban",
+	"cel-gaulish",
+	"en-GB-oed",
+	"i-ami",
+	"i-bnn",
+	"i-default",
+	"i-enochian",
+	"i-hak",
+	"i-klingon",
+	"i-lux",
+	"i-mingo",
+	"i-navajo",
+	"i-pwn",
+	"i-tao",
+	"i-tay",
+	"i-tsu",
+	"no-bok",
+	"no-nyn",
+	"sgn-BE-FR",
+	"sgn-BE-NL",
+	"sgn-BR",
+	"sgn-CH-DE",
+	"sgn-CO",
+	"sgn-DE",
+	"sgn-DK",
+	"sgn-ES",
+	"sgn-FR",
+	"sgn-GB",
+	"sgn-GR",
+	"sgn-IE",
+	"sgn-IT",
+	"sgn-JP",
+	"sgn-MX",
+	"sgn-NI",
+	"sgn-NL",
+	"sgn-NO",
+	"sgn-PT",
+	"sgn-SE",
+	"sgn-US",
+	"sgn-ZA",
+	"zh-cmn",
+	"zh-cmn-Hans",
+	"zh-cmn-Hant",
+	"zh-gan",
+	"zh-guoyu",
+	"zh-hakka",
+	"zh-min",
+	"zh-min-nan",
+	"zh-wuu",
+	"zh-xiang",
+	NULL
 };
 
-/* Based on IANA registry at the time of writing this code
-*  This array lists the preferred values for the grandfathered tags if applicable
-*  This is in sync with the array LOC_GRANDFATHERED
-*  e.g. the offsets of the grandfathered tags match the offset of the preferred  value
-*/
-static const int 		LOC_PREFERRED_GRANDFATHERED_LEN = 6;
-static const char * const 	LOC_PREFERRED_GRANDFATHERED[]  = {
-	"jbo",			"tlh",			"lb",
-	"nv", 			"nb",			"nn",
+/* Based on the IANA language subtag registry (File-Date: 2021-08-06)
+ *
+ * This array lists the preferred values for the grandfathered and redundant
+ * tags listed in LOC_GRANDFATHERED. This is in sync with the array
+ * LOC_GRANDFATHERED, i.e., the offsets of the grandfathered tags match the
+ * offsets of the preferred value. If a value in LOC_PREFERRED_GRANDFATHERED is
+ * NULL, then the matching offset in LOC_GRANDFATHERED has no preferred value.
+ */
+static const char * const LOC_PREFERRED_GRANDFATHERED[] = {
+	"jbo",
+	NULL,
+	"en-GB-oxendict",
+	"ami",
+	"bnn",
+	NULL,
+	NULL,
+	"hak",
+	"tlh",
+	"lb",
+	NULL,
+	"nv",
+	"pwn",
+	"tao",
+	"tay",
+	"tsu",
+	"nb",
+	"nn",
+	"sfb",
+	"vgt",
+	"bzs",
+	"sgg",
+	"csn",
+	"gsg",
+	"dsl",
+	"ssp",
+	"fsl",
+	"bfi",
+	"gss",
+	"isg",
+	"ise",
+	"jsl",
+	"mfs",
+	"ncs",
+	"dse",
+	"nsl",
+	"psr",
+	"swl",
+	"ase",
+	"sfs",
+	"cmn",
+	"cmn-Hans",
+	"cmn-Hant",
+	"gan",
+	"cmn",
+	"hak",
+	NULL,
+	"nan",
+	"wuu",
+	"hsn",
 	NULL
 };
 
@@ -105,7 +199,7 @@ static int16_t findOffset(const char* const* list, const char* key)
 {
 	const char* const* anchor = list;
 	while (*list != NULL) {
-		if (strcmp(key, *list) == 0) {
+		if (strcasecmp(key, *list) == 0) {
 			return (int16_t)(list - anchor);
 		}
 		list++;
@@ -125,7 +219,7 @@ static char* getPreferredTag(const char* gf_tag)
 	if(grOffset < 0) {
 		return NULL;
 	}
-	if( grOffset < LOC_PREFERRED_GRANDFATHERED_LEN ){
+	if( LOC_PREFERRED_GRANDFATHERED[grOffset] != NULL ){
 		/* return preferred tag */
 		result = estrdup( LOC_PREFERRED_GRANDFATHERED[grOffset] );
 	} else {
@@ -503,7 +597,7 @@ static void get_icu_disp_value_src_php( char* tag_name, INTERNAL_FUNCTION_PARAME
 			if( strcmp(tag_name , LOC_LANG_TAG)==0 ){
 				mod_loc_name = getPreferredTag( loc_name );
 			} else {
-				/* Since Grandfathered, no value, do nothing, retutn NULL */
+				/* Since Grandfathered, no value, do nothing, return NULL */
 				RETURN_FALSE;
 			}
 		}
diff --git a/ext/intl/tests/locale_get_display_language3.phpt b/ext/intl/tests/locale_get_display_language3.phpt
new file mode 100644
index 00000000000..9924e543cb6
--- /dev/null
+++ b/ext/intl/tests/locale_get_display_language3.phpt
@@ -0,0 +1,338 @@
+--TEST--
+locale_get_display_language() for grandfathered and redundant tags
+--EXTENSIONS--
+intl
+--FILE--
+<?php
+
+function ut_main()
+{
+    $res_str = '';
+    $disp_locales = ['en', 'fr', 'de'];
+
+    // This array includes all grandfathered tags, as well as any redundant tags
+    // that have a Preferred-Value.
+    // See: https://www.iana.org/assignments/language-subtag-registry/
+    $locales = [
+        'art-lojban',
+        'cel-gaulish',
+        'en-GB-oed',
+        'i-ami',
+        'i-bnn',
+        'i-default',
+        'i-enochian',
+        'i-hak',
+        'i-klingon',
+        'i-lux',
+        'i-mingo',
+        'i-navajo',
+        'i-pwn',
+        'i-tao',
+        'i-tay',
+        'i-tsu',
+        'no-bok',
+        'no-nyn',
+        'sgn-BE-FR',
+        'sgn-BE-NL',
+        'sgn-BR',
+        'sgn-CH-DE',
+        'sgn-CO',
+        'sgn-DE',
+        'sgn-DK',
+        'sgn-ES',
+        'sgn-FR',
+        'sgn-GB',
+        'sgn-GR',
+        'sgn-IE',
+        'sgn-IT',
+        'sgn-JP',
+        'sgn-MX',
+        'sgn-NI',
+        'sgn-NL',
+        'sgn-NO',
+        'sgn-PT',
+        'sgn-SE',
+        'sgn-US',
+        'sgn-ZA',
+        'zh-cmn',
+        'zh-cmn-Hans',
+        'zh-cmn-Hant',
+        'zh-gan',
+        'zh-guoyu',
+        'zh-hakka',
+        'zh-min',
+        'zh-min-nan',
+        'zh-wuu',
+        'zh-xiang',
+    ];
+
+    foreach ($locales as $locale) {
+        $res_str .= "locale='$locale'\n";
+
+        foreach ($disp_locales as $disp_locale) {
+            $scr = ut_loc_get_display_language($locale, $disp_locale);
+            $res_str .= "disp_locale=$disp_locale :  display_language=$scr";
+            $res_str .= "\n";
+        }
+
+        $res_str .= "-----------------\n";
+    }
+
+    return $res_str;
+}
+
+include_once 'ut_common.inc';
+ut_run();
+
+?>
+--EXPECTREGEX--
+locale='art-lojban'
+disp_locale=en :  display_language=Lojban
+disp_locale=fr :  display_language=lojban
+disp_locale=de :  display_language=Lojban
+-----------------
+locale='cel-gaulish'
+disp_locale=en :  display_language=cel
+disp_locale=fr :  display_language=cel
+disp_locale=de :  display_language=cel
+-----------------
+locale='en-GB-oed'
+disp_locale=en :  display_language=English
+disp_locale=fr :  display_language=anglais
+disp_locale=de :  display_language=Englisch
+-----------------
+locale='i-ami'
+disp_locale=en :  display_language=ami
+disp_locale=fr :  display_language=ami
+disp_locale=de :  display_language=ami
+-----------------
+locale='i-bnn'
+disp_locale=en :  display_language=bnn
+disp_locale=fr :  display_language=bnn
+disp_locale=de :  display_language=bnn
+-----------------
+locale='i-default'
+disp_locale=en :  display_language=i-default
+disp_locale=fr :  display_language=i-default
+disp_locale=de :  display_language=i-default
+-----------------
+locale='i-enochian'
+disp_locale=en :  display_language=i-enochian
+disp_locale=fr :  display_language=i-enochian
+disp_locale=de :  display_language=i-enochian
+-----------------
+locale='i-hak'
+disp_locale=en :  display_language=Hakka Chinese
+disp_locale=fr :  display_language=hakka
+disp_locale=de :  display_language=Hakka
+-----------------
+locale='i-klingon'
+disp_locale=en :  display_language=Klingon
+disp_locale=fr :  display_language=klingon
+disp_locale=de :  display_language=Klingonisch
+-----------------
+locale='i-lux'
+disp_locale=en :  display_language=Luxembourgish
+disp_locale=fr :  display_language=luxembourgeois
+disp_locale=de :  display_language=Luxemburgisch
+-----------------
+locale='i-mingo'
+disp_locale=en :  display_language=i-mingo
+disp_locale=fr :  display_language=i-mingo
+disp_locale=de :  display_language=i-mingo
+-----------------
+locale='i-navajo'
+disp_locale=en :  display_language=Navajo
+disp_locale=fr :  display_language=navajo
+disp_locale=de :  display_language=Navajo
+-----------------
+locale='i-pwn'
+disp_locale=en :  display_language=pwn
+disp_locale=fr :  display_language=pwn
+disp_locale=de :  display_language=pwn
+-----------------
+locale='i-tao'
+disp_locale=en :  display_language=tao
+disp_locale=fr :  display_language=tao
+disp_locale=de :  display_language=tao
+-----------------
+locale='i-tay'
+disp_locale=en :  display_language=tay
+disp_locale=fr :  display_language=tay
+disp_locale=de :  display_language=tay
+-----------------
+locale='i-tsu'
+disp_locale=en :  display_language=tsu
+disp_locale=fr :  display_language=tsu
+disp_locale=de :  display_language=tsu
+-----------------
+locale='no-bok'
+disp_locale=en :  display_language=Norwegian Bokmål
+disp_locale=fr :  display_language=norvégien bokmål
+disp_locale=de :  display_language=Norwegisch \(?Bokmål\)?
+-----------------
+locale='no-nyn'
+disp_locale=en :  display_language=Norwegian Nynorsk
+disp_locale=fr :  display_language=norvégien nynorsk
+disp_locale=de :  display_language=Norwegisch \(?Nynorsk\)?
+-----------------
+locale='sgn-BE-FR'
+disp_locale=en :  display_language=sfb
+disp_locale=fr :  display_language=sfb
+disp_locale=de :  display_language=sfb
+-----------------
+locale='sgn-BE-NL'
+disp_locale=en :  display_language=vgt
+disp_locale=fr :  display_language=vgt
+disp_locale=de :  display_language=vgt
+-----------------
+locale='sgn-BR'
+disp_locale=en :  display_language=bzs
+disp_locale=fr :  display_language=bzs
+disp_locale=de :  display_language=bzs
+-----------------
+locale='sgn-CH-DE'
+disp_locale=en :  display_language=sgg
+disp_locale=fr :  display_language=sgg
+disp_locale=de :  display_language=sgg
+-----------------
+locale='sgn-CO'
+disp_locale=en :  display_language=csn
+disp_locale=fr :  display_language=csn
+disp_locale=de :  display_language=csn
+-----------------
+locale='sgn-DE'
+disp_locale=en :  display_language=gsg
+disp_locale=fr :  display_language=gsg
+disp_locale=de :  display_language=gsg
+-----------------
+locale='sgn-DK'
+disp_locale=en :  display_language=dsl
+disp_locale=fr :  display_language=dsl
+disp_locale=de :  display_language=dsl
+-----------------
+locale='sgn-ES'
+disp_locale=en :  display_language=ssp
+disp_locale=fr :  display_language=ssp
+disp_locale=de :  display_language=ssp
+-----------------
+locale='sgn-FR'
+disp_locale=en :  display_language=fsl
+disp_locale=fr :  display_language=fsl
+disp_locale=de :  display_language=fsl
+-----------------
+locale='sgn-GB'
+disp_locale=en :  display_language=bfi
+disp_locale=fr :  display_language=bfi
+disp_locale=de :  display_language=bfi
+-----------------
+locale='sgn-GR'
+disp_locale=en :  display_language=gss
+disp_locale=fr :  display_language=gss
+disp_locale=de :  display_language=gss
+-----------------
+locale='sgn-IE'
+disp_locale=en :  display_language=isg
+disp_locale=fr :  display_language=isg
+disp_locale=de :  display_language=isg
+-----------------
+locale='sgn-IT'
+disp_locale=en :  display_language=ise
+disp_locale=fr :  display_language=ise
+disp_locale=de :  display_language=ise
+-----------------
+locale='sgn-JP'
+disp_locale=en :  display_language=jsl
+disp_locale=fr :  display_language=jsl
+disp_locale=de :  display_language=jsl
+-----------------
+locale='sgn-MX'
+disp_locale=en :  display_language=mfs
+disp_locale=fr :  display_language=mfs
+disp_locale=de :  display_language=mfs
+-----------------
+locale='sgn-NI'
+disp_locale=en :  display_language=ncs
+disp_locale=fr :  display_language=ncs
+disp_locale=de :  display_language=ncs
+-----------------
+locale='sgn-NL'
+disp_locale=en :  display_language=dse
+disp_locale=fr :  display_language=dse
+disp_locale=de :  display_language=dse
+-----------------
+locale='sgn-NO'
+disp_locale=en :  display_language=nsl
+disp_locale=fr :  display_language=nsl
+disp_locale=de :  display_language=nsl
+-----------------
+locale='sgn-PT'
+disp_locale=en :  display_language=psr
+disp_locale=fr :  display_language=psr
+disp_locale=de :  display_language=psr
+-----------------
+locale='sgn-SE'
+disp_locale=en :  display_language=swl
+disp_locale=fr :  display_language=swl
+disp_locale=de :  display_language=swl
+-----------------
+locale='sgn-US'
+disp_locale=en :  display_language=American Sign Language
+disp_locale=fr :  display_language=langue des signes américaine
+disp_locale=de :  display_language=Amerikanische Gebärdensprache
+-----------------
+locale='sgn-ZA'
+disp_locale=en :  display_language=sfs
+disp_locale=fr :  display_language=sfs
+disp_locale=de :  display_language=sfs
+-----------------
+locale='zh-cmn'
+disp_locale=en :  display_language=(cmn|Chinese)
+disp_locale=fr :  display_language=(cmn|chinois)
+disp_locale=de :  display_language=(cmn|Chinesisch)
+-----------------
+locale='zh-cmn-Hans'
+disp_locale=en :  display_language=(cmn|Chinese)
+disp_locale=fr :  display_language=(cmn|chinois)
+disp_locale=de :  display_language=(cmn|Chinesisch)
+-----------------
+locale='zh-cmn-Hant'
+disp_locale=en :  display_language=(cmn|Chinese)
+disp_locale=fr :  display_language=(cmn|chinois)
+disp_locale=de :  display_language=(cmn|Chinesisch)
+-----------------
+locale='zh-gan'
+disp_locale=en :  display_language=Gan Chinese
+disp_locale=fr :  display_language=gan
+disp_locale=de :  display_language=Gan
+-----------------
+locale='zh-guoyu'
+disp_locale=en :  display_language=(cmn|Chinese)
+disp_locale=fr :  display_language=(cmn|chinois)
+disp_locale=de :  display_language=(cmn|Chinesisch)
+-----------------
+locale='zh-hakka'
+disp_locale=en :  display_language=Hakka Chinese
+disp_locale=fr :  display_language=hakka
+disp_locale=de :  display_language=Hakka
+-----------------
+locale='zh-min'
+disp_locale=en :  display_language=Chinese
+disp_locale=fr :  display_language=chinois
+disp_locale=de :  display_language=Chinesisch
+-----------------
+locale='zh-min-nan'
+disp_locale=en :  display_language=Min Nan Chinese
+disp_locale=fr :  display_language=minnan
+disp_locale=de :  display_language=Min Nan
+-----------------
+locale='zh-wuu'
+disp_locale=en :  display_language=Wu Chinese
+disp_locale=fr :  display_language=wu
+disp_locale=de :  display_language=Wu
+-----------------
+locale='zh-xiang'
+disp_locale=en :  display_language=Xiang Chinese
+disp_locale=fr :  display_language=xiang
+disp_locale=de :  display_language=Xiang
+-----------------