diff --git a/icu4c/source/common/ucurr.cpp b/icu4c/source/common/ucurr.cpp
index a2f4fb30e1f..70b1bbf2239 100644
--- a/icu4c/source/common/ucurr.cpp
+++ b/icu4c/source/common/ucurr.cpp
@@ -11,6 +11,8 @@
 
 #if !UCONFIG_NO_FORMATTING
 
+#include <utility>
+
 #include "unicode/ucurr.h"
 #include "unicode/locid.h"
 #include "unicode/ures.h"
@@ -602,11 +604,15 @@ ucurr_forLocale(const char* locale,
 
     if ((U_FAILURE(localStatus)) && strchr(id, '_') != 0) {
         // We don't know about it.  Check to see if we support the variant.
-        uloc_getParent(locale, id, UPRV_LENGTHOF(id), ec);
+        CharString parent;
+        {
+            CharStringByteSink sink(&parent);
+            ulocimp_getParent(locale, sink, ec);
+        }
         *ec = U_USING_FALLBACK_WARNING;
-        // TODO: Loop over the shortened id rather than recursing and
+        // TODO: Loop over the parent rather than recursing and
         // looking again for a currency keyword.
-        return ucurr_forLocale(id, buff, buffCapacity, ec);
+        return ucurr_forLocale(parent.data(), buff, buffCapacity, ec);
     }
     if (*ec == U_ZERO_ERROR || localStatus != U_ZERO_ERROR) {
         // There is nothing to fallback to. Report the failure/warning if possible.
@@ -629,20 +635,22 @@ ucurr_forLocale(const char* locale,
  * @return true if the fallback happened; false if locale is already
  * root ("").
  */
-static UBool fallback(char *loc) {
-    if (!*loc) {
+static UBool fallback(CharString& loc) {
+    if (loc.isEmpty()) {
         return false;
     }
     UErrorCode status = U_ZERO_ERROR;
-    if (uprv_strcmp(loc, "en_GB") == 0) {
+    if (loc == "en_GB") {
         // HACK: See #13368.  We need "en_GB" to fall back to "en_001" instead of "en"
         // in order to consume the correct data strings.  This hack will be removed
         // when proper data sink loading is implemented here.
-        // NOTE: "001" adds 1 char over "GB".  However, both call sites allocate
-        // arrays with length ULOC_FULLNAME_CAPACITY (plenty of room for en_001).
-        uprv_strcpy(loc + 3, "001");
+        loc.truncate(3);
+        loc.append("001", status);
     } else {
-        uloc_getParent(loc, loc, (int32_t)uprv_strlen(loc), &status);
+        CharString tmp;
+        CharStringByteSink sink(&tmp);
+        ulocimp_getParent(loc.data(), sink, &status);
+        loc = std::move(tmp);
     }
  /*
     char *i = uprv_strrchr(loc, '_');
@@ -915,13 +923,17 @@ getCurrencyNameCount(const char* loc, int32_t* total_currency_name_count, int32_
     *total_currency_name_count = 0;
     *total_currency_symbol_count = 0;
     const char16_t* s = nullptr;
-    char locale[ULOC_FULLNAME_CAPACITY] = "";
-    uprv_strcpy(locale, loc);
+    CharString locale;
+    {
+        UErrorCode status = U_ZERO_ERROR;
+        locale.append(loc, status);
+        if (U_FAILURE(status)) { return; }
+    }
     const icu::Hashtable *currencySymbolsEquiv = getCurrSymbolsEquiv();
     for (;;) {
         UErrorCode ec2 = U_ZERO_ERROR;
         // TODO: ures_openDirect?
-        UResourceBundle* rb = ures_open(U_ICUDATA_CURR, locale, &ec2);
+        UResourceBundle* rb = ures_open(U_ICUDATA_CURR, locale.data(), &ec2);
         UResourceBundle* curr = ures_getByKey(rb, CURRENCIES, nullptr, &ec2);
         int32_t n = ures_getSize(curr);
         for (int32_t i=0; i<n; ++i) {
@@ -1122,7 +1134,7 @@ collectCurrencyNames(const char* locale,
         ures_close(curr);
         ures_close(rb);
 
-        if (!fallback(loc.data())) {
+        if (!fallback(loc)) {
             break;
         }
     }
diff --git a/icu4c/source/common/uloc.cpp b/icu4c/source/common/uloc.cpp
index becba3e9f6f..45990288847 100644
--- a/icu4c/source/common/uloc.cpp
+++ b/icu4c/source/common/uloc.cpp
@@ -1655,12 +1655,39 @@ uloc_getParent(const char*    localeID,
                char* parent,
                int32_t parentCapacity,
                UErrorCode* err)
+{
+    if (U_FAILURE(*err)) {
+        return 0;
+    }
+
+    CheckedArrayByteSink sink(parent, parentCapacity);
+    ulocimp_getParent(localeID, sink, err);
+
+    int32_t reslen = sink.NumberOfBytesAppended();
+
+    if (U_FAILURE(*err)) {
+        return reslen;
+    }
+
+    if (sink.Overflowed()) {
+        *err = U_BUFFER_OVERFLOW_ERROR;
+    } else {
+        u_terminateChars(parent, parentCapacity, reslen, err);
+    }
+
+    return reslen;
+}
+
+U_CAPI void U_EXPORT2
+ulocimp_getParent(const char* localeID,
+                  icu::ByteSink& sink,
+                  UErrorCode* err)
 {
     const char *lastUnderscore;
     int32_t i;
 
     if (U_FAILURE(*err))
-        return 0;
+        return;
 
     if (localeID == nullptr)
         localeID = uloc_getDefault();
@@ -1676,13 +1703,9 @@ uloc_getParent(const char*    localeID,
         if (uprv_strnicmp(localeID, "und_", 4) == 0) {
             localeID += 3;
             i -= 3;
-            uprv_memmove(parent, localeID, uprv_min(i, parentCapacity));
-        } else if (parent != localeID) {
-            uprv_memcpy(parent, localeID, uprv_min(i, parentCapacity));
         }
+        sink.Append(localeID, i);
     }
-
-    return u_terminateChars(parent, parentCapacity, i, err);
 }
 
 U_CAPI int32_t U_EXPORT2
diff --git a/icu4c/source/common/ulocimp.h b/icu4c/source/common/ulocimp.h
index 4ab4cb1feb6..efa0fa72e6a 100644
--- a/icu4c/source/common/ulocimp.h
+++ b/icu4c/source/common/ulocimp.h
@@ -92,6 +92,11 @@ ulocimp_getKeywordValue(const char* localeID,
                         icu::ByteSink& sink,
                         UErrorCode* status);
 
+U_CAPI void U_EXPORT2
+ulocimp_getParent(const char* localeID,
+                  icu::ByteSink& sink,
+                  UErrorCode* err);
+
 /**
  * Writes a well-formed language tag for this locale ID.
  *
diff --git a/icu4c/source/i18n/dayperiodrules.cpp b/icu4c/source/i18n/dayperiodrules.cpp
index 3d9ab5bfac5..294390cce2b 100644
--- a/icu4c/source/i18n/dayperiodrules.cpp
+++ b/icu4c/source/i18n/dayperiodrules.cpp
@@ -14,10 +14,12 @@
 #include "dayperiodrules.h"
 
 #include "unicode/ures.h"
+#include "bytesinkutil.h"
 #include "charstr.h"
 #include "cstring.h"
 #include "ucln_in.h"
 #include "uhash.h"
+#include "ulocimp.h"
 #include "umutex.h"
 #include "uresimp.h"
 
@@ -342,7 +344,6 @@ const DayPeriodRules *DayPeriodRules::getInstance(const Locale &locale, UErrorCo
 
     const char *localeCode = locale.getBaseName();
     char name[ULOC_FULLNAME_CAPACITY];
-    char parentName[ULOC_FULLNAME_CAPACITY];
 
     if (uprv_strlen(localeCode) < ULOC_FULLNAME_CAPACITY) {
         uprv_strcpy(name, localeCode);
@@ -360,13 +361,14 @@ const DayPeriodRules *DayPeriodRules::getInstance(const Locale &locale, UErrorCo
     while (*name != '\0') {
         ruleSetNum = uhash_geti(data->localeToRuleSetNumMap, name);
         if (ruleSetNum == 0) {
-            // name and parentName can't be the same pointer, so fill in parent then copy to child.
-            uloc_getParent(name, parentName, ULOC_FULLNAME_CAPACITY, &errorCode);
-            if (*parentName == '\0') {
+            CharString parent;
+            CharStringByteSink sink(&parent);
+            ulocimp_getParent(name, sink, &errorCode);
+            if (parent.isEmpty()) {
                 // Saves a lookup in the hash table.
                 break;
             }
-            uprv_strcpy(name, parentName);
+            parent.extract(name, UPRV_LENGTHOF(name), errorCode);
         } else {
             break;
         }
diff --git a/icu4c/source/i18n/gender.cpp b/icu4c/source/i18n/gender.cpp
index 97d161de321..d023b50218a 100644
--- a/icu4c/source/i18n/gender.cpp
+++ b/icu4c/source/i18n/gender.cpp
@@ -19,15 +19,20 @@
 
 #if !UCONFIG_NO_FORMATTING
 
+#include <utility>
+
 #include "unicode/gender.h"
 #include "unicode/ugender.h"
 #include "unicode/ures.h"
 
+#include "bytesinkutil.h"
+#include "charstr.h"
 #include "cmemory.h"
 #include "cstring.h"
 #include "mutex.h"
 #include "uassert.h"
 #include "ucln_in.h"
+#include "ulocimp.h"
 #include "umutex.h"
 #include "uhash.h"
 
@@ -148,12 +153,18 @@ const GenderInfo* GenderInfo::loadInstance(const Locale& locale, UErrorCode& sta
   const char16_t* s = ures_getStringByKey(locRes.getAlias(), curLocaleName, &resLen, &key_status);
   if (s == nullptr) {
     key_status = U_ZERO_ERROR;
-    char parentLocaleName[ULOC_FULLNAME_CAPACITY];
-    uprv_strcpy(parentLocaleName, curLocaleName);
-    while (s == nullptr && uloc_getParent(parentLocaleName, parentLocaleName, ULOC_FULLNAME_CAPACITY, &key_status) > 0) {
+    CharString parentLocaleName(curLocaleName, key_status);
+    while (s == nullptr) {
+      {
+        CharString tmp;
+        CharStringByteSink sink(&tmp);
+        ulocimp_getParent(parentLocaleName.data(), sink, &status);
+        if (tmp.isEmpty()) break;
+        parentLocaleName = std::move(tmp);
+      }
       key_status = U_ZERO_ERROR;
       resLen = 0;
-      s = ures_getStringByKey(locRes.getAlias(), parentLocaleName, &resLen, &key_status);
+      s = ures_getStringByKey(locRes.getAlias(), parentLocaleName.data(), &resLen, &key_status);
       key_status = U_ZERO_ERROR;
     }
   }
diff --git a/icu4c/source/i18n/plurrule.cpp b/icu4c/source/i18n/plurrule.cpp
index 9c37b09e253..839d14147cc 100644
--- a/icu4c/source/i18n/plurrule.cpp
+++ b/icu4c/source/i18n/plurrule.cpp
@@ -12,6 +12,8 @@
 #include <math.h>
 #include <stdio.h>
 
+#include <utility>
+
 #include "unicode/utypes.h"
 #include "unicode/localpointer.h"
 #include "unicode/plurrule.h"
@@ -20,6 +22,7 @@
 #include "unicode/numfmt.h"
 #include "unicode/decimfmt.h"
 #include "unicode/numberrangeformatter.h"
+#include "bytesinkutil.h"
 #include "charstr.h"
 #include "cmemory.h"
 #include "cstring.h"
@@ -40,6 +43,7 @@
 #include "util.h"
 #include "pluralranges.h"
 #include "numrange_impl.h"
+#include "ulocimp.h"
 
 #if !UCONFIG_NO_FORMATTING
 
@@ -827,14 +831,19 @@ PluralRules::getRuleFromResource(const Locale& locale, UPluralType type, UErrorC
     if (s == nullptr) {
         // Check parent locales.
         UErrorCode status = U_ZERO_ERROR;
-        char parentLocaleName[ULOC_FULLNAME_CAPACITY];
         const char *curLocaleName2=locale.getBaseName();
-        uprv_strcpy(parentLocaleName, curLocaleName2);
+        CharString parentLocaleName(curLocaleName2, status);
 
-        while (uloc_getParent(parentLocaleName, parentLocaleName,
-                                       ULOC_FULLNAME_CAPACITY, &status) > 0) {
+        for (;;) {
+            {
+                CharString tmp;
+                CharStringByteSink sink(&tmp);
+                ulocimp_getParent(parentLocaleName.data(), sink, &status);
+                if (tmp.isEmpty()) break;
+                parentLocaleName = std::move(tmp);
+            }
             resLen=0;
-            s = ures_getStringByKey(locRes.getAlias(), parentLocaleName, &resLen, &status);
+            s = ures_getStringByKey(locRes.getAlias(), parentLocaleName.data(), &resLen, &status);
             if (s != nullptr) {
                 errCode = U_ZERO_ERROR;
                 break;
diff --git a/icu4c/source/i18n/tmutfmt.cpp b/icu4c/source/i18n/tmutfmt.cpp
index 87b509ea35c..dc48b2ee2a4 100644
--- a/icu4c/source/i18n/tmutfmt.cpp
+++ b/icu4c/source/i18n/tmutfmt.cpp
@@ -11,14 +11,18 @@
 
 #if !UCONFIG_NO_FORMATTING
 
+#include <utility>
+
 #include "unicode/decimfmt.h"
 #include "unicode/localpointer.h"
 #include "plurrule_impl.h"
 #include "uvector.h"
+#include "bytesinkutil.h"
 #include "charstr.h"
 #include "cmemory.h"
 #include "cstring.h"
 #include "hash.h"
+#include "ulocimp.h"
 #include "uresimp.h"
 #include "ureslocs.h"
 #include "unicode/msgfmt.h"
@@ -556,14 +560,17 @@ TimeUnitFormat::searchInLocaleChain(UTimeUnitFormatStyle style, const char* key,
         return;
     }
     UErrorCode status = U_ZERO_ERROR;
-    char parentLocale[ULOC_FULLNAME_CAPACITY];
-    uprv_strcpy(parentLocale, localeName);
-    int32_t locNameLen;
+    CharString parentLocale(localeName, status);
     U_ASSERT(countToPatterns != nullptr);
-    while ((locNameLen = uloc_getParent(parentLocale, parentLocale,
-                                        ULOC_FULLNAME_CAPACITY, &status)) >= 0){
+    for (;;) {
+        {
+            CharString tmp;
+            CharStringByteSink sink(&tmp);
+            ulocimp_getParent(parentLocale.data(), sink, &status);
+            parentLocale = std::move(tmp);
+        }
         // look for pattern for srcPluralCount in locale tree
-        LocalUResourceBundlePointer rb(ures_open(U_ICUDATA_UNIT, parentLocale, &status));
+        LocalUResourceBundlePointer rb(ures_open(U_ICUDATA_UNIT, parentLocale.data(), &status));
         LocalUResourceBundlePointer unitsRes(ures_getByKey(rb.getAlias(), key, nullptr, &status));
         const char* timeUnitName = getTimeUnitName(srcTimeUnitField, status);
         LocalUResourceBundlePointer countsToPatternRB(ures_getByKey(unitsRes.getAlias(), timeUnitName, nullptr, &status));
@@ -594,14 +601,14 @@ TimeUnitFormat::searchInLocaleChain(UTimeUnitFormatStyle style, const char* key,
             return;
         }
         status = U_ZERO_ERROR;
-        if (locNameLen == 0) {
+        if (parentLocale.isEmpty()) {
             break;
         }
     }
 
     // if no unitsShort resource was found even after fallback to root locale
     // then search the units resource fallback from the current level to root
-    if ( locNameLen == 0 && uprv_strcmp(key, gShortUnitsTag) == 0) {
+    if ( parentLocale.isEmpty() && uprv_strcmp(key, gShortUnitsTag) == 0) {
 #ifdef TMUTFMT_DEBUG
         std::cout << "loop into searchInLocaleChain since Short-Long-Alternative \n";
 #endif