diff --git a/src/common/bcp47.cpp b/src/common/bcp47.cpp
index 27040feaa..4eb330173 100644
--- a/src/common/bcp47.cpp
+++ b/src/common/bcp47.cpp
@@ -783,6 +783,79 @@ language_c::find_best_match(std::vector<language_c> const &potential_matches)
   return best_match;
 }
 
+language_c &
+language_c::canonicalize_preferred_values() {
+  auto &preferred_values = mtx::iana::language_subtag_registry::g_preferred_values;
+  auto idx               = std::find_if(preferred_values.begin(), preferred_values.end(),
+                                        [this](auto const &pair) {
+                                          return matches(pair.first);
+                                        });
+
+  if (idx == preferred_values.end())
+    return *this;
+
+  // mxdebug(fmt::format("found one! I am {0} first is {1} second {2}\n", dump(), idx->first.dump(), idx->second.dump()));
+
+  auto const &[match, preferred] = *idx;
+
+  if (!preferred.m_language.empty()) {
+    if (!match.m_language.empty())
+      m_language.clear();
+
+    if (!match.m_extended_language_subtags.empty())
+      m_extended_language_subtags.clear();
+
+    if (!match.m_script.empty())
+      m_script.clear();
+
+    if (!match.m_region.empty())
+      m_region.clear();
+
+    if (!match.m_variants.empty())
+      m_variants.clear();
+
+    if (!match.m_extensions.empty())
+      m_extensions.clear();
+
+    if (!match.m_private_use.empty())
+      m_private_use.clear();
+
+    if (!match.m_grandfathered.empty())
+      m_grandfathered.clear();
+  }
+
+  if (!preferred.m_language.empty())
+    m_language = preferred.m_language;
+
+  if (!preferred.m_extended_language_subtags.empty())
+    m_extended_language_subtags = preferred.m_extended_language_subtags;
+
+  if (!preferred.m_script.empty())
+    m_script = preferred.m_script;
+
+  if (!preferred.m_region.empty())
+    m_region = preferred.m_region;
+
+  if (!preferred.m_variants.empty())
+    m_variants = preferred.m_variants;
+
+  if (!preferred.m_extensions.empty())
+    m_extensions = preferred.m_extensions;
+
+  if (!preferred.m_private_use.empty())
+    m_private_use = preferred.m_private_use;
+
+  if (!preferred.m_grandfathered.empty())
+    m_grandfathered = preferred.m_grandfathered;
+
+  return *this;
+}
+
+language_c &
+language_c::to_canonical_form() {
+  return canonicalize_preferred_values();
+}
+
 void
 language_c::disable() {
   ms_disabled = true;
diff --git a/src/common/bcp47.h b/src/common/bcp47.h
index fe01f814b..af4f20359 100644
--- a/src/common/bcp47.h
+++ b/src/common/bcp47.h
@@ -77,6 +77,8 @@ public:
   bool matches(language_c const &match) const noexcept;
   language_c find_best_match(std::vector<language_c> const &potential_matches) const noexcept;
 
+  language_c &to_canonical_form();
+
   language_c &set_valid(bool valid);
   language_c &set_language(std::string const &language);
   language_c &set_extended_language_subtags(std::vector<std::string> const &extended_language_subtags);
@@ -113,6 +115,8 @@ protected:
   bool validate_one_extlang(std::size_t extlang_index);
   bool matches_prefix(language_c const &prefix, std::size_t extlang_index, prefix_restrictions_t const &restrictions) const noexcept;
 
+  language_c &canonicalize_preferred_values();
+
 public:
   static language_c parse(std::string const &language);
 
diff --git a/tests/unit/common/bcp47.cpp b/tests/unit/common/bcp47.cpp
index 4edd439d9..9e9032166 100644
--- a/tests/unit/common/bcp47.cpp
+++ b/tests/unit/common/bcp47.cpp
@@ -423,4 +423,26 @@ TEST(BCP47LanguageTags, Grandfathered) {
   EXPECT_EQ("i-KLINGON"s, l.get_grandfathered());
 }
 
+TEST(BCP47LanguageTags, ToCanonicalForm) {
+  // No changes as they're already normalized.
+  EXPECT_EQ("sgn"s, language_c::parse("sgn"s).to_canonical_form().format());
+  EXPECT_EQ("nsi"s, language_c::parse("nsi"s).to_canonical_form().format());
+
+  // No changes as even though they're listed as redundant, they don't have preferred values.
+  EXPECT_EQ("az-Arab"s, language_c::parse("az-Arab"s).to_canonical_form().format());
+
+  // For the following there are changes.
+  EXPECT_EQ("nsi"s,             language_c::parse("sgn-nsi"s).to_canonical_form().format());
+  EXPECT_EQ("ja-Latn-alalc97"s, language_c::parse("ja-Latn-hepburn-heploc"s).to_canonical_form().format());
+  EXPECT_EQ("jbo"s,             language_c::parse("art-lojban"s).to_canonical_form().format());
+  EXPECT_EQ("jsl"s,             language_c::parse("sgn-JP"s).to_canonical_form().format());
+  EXPECT_EQ("cmn"s,             language_c::parse("zh-cmn"s).to_canonical_form().format());
+  EXPECT_EQ("cmn-CN"s,          language_c::parse("zh-cmn-CN"s).to_canonical_form().format());
+  EXPECT_EQ("cmn-Hans"s,        language_c::parse("zh-cmn-Hans"s).to_canonical_form().format());
+  EXPECT_EQ("cmn"s,             language_c::parse("zh-guoyu"s).to_canonical_form().format());
+  EXPECT_EQ("hak"s,             language_c::parse("zh-hakka"s).to_canonical_form().format());
+  EXPECT_EQ("hak"s,             language_c::parse("i-hak"s).to_canonical_form().format());
+  EXPECT_EQ("yue-jyutping"s,    language_c::parse("zh-yue-jyutping"s).to_canonical_form().format());
+}
+
 }