diff --git a/packages/react-native/React/I18n/.clang-format-ignore b/packages/react-native/React/I18n/.clang-format-ignore
new file mode 100644
index 00000000000..63b7f47b0fb
--- /dev/null
+++ b/packages/react-native/React/I18n/.clang-format-ignore
@@ -0,0 +1,2 @@
+# Synced externally
+FBXXHashUtils.h
diff --git a/packages/react-native/React/I18n/FBXXHashUtils.h b/packages/react-native/React/I18n/FBXXHashUtils.h
new file mode 100644
index 00000000000..abfa11a8c5f
--- /dev/null
+++ b/packages/react-native/React/I18n/FBXXHashUtils.h
@@ -0,0 +1,118 @@
+/*
+ * Copyright (c) 2015 Daniel Kirchner
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+// Based on implementation: https://github.com/ekpyron/xxhashct/blob/master/xxh64.hpp
+// To generate string hash at compile time, the original file has been slightly modified by i18n team.
+
+#import <Foundation/Foundation.h>
+
+NS_ASSUME_NONNULL_BEGIN
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/// magic constants :-)
+static const uint64_t PRIME1 = 11400714785074694791ULL;
+static const uint64_t PRIME2 = 14029467366897019727ULL;
+static const uint64_t PRIME3 = 1609587929392839161ULL;
+static const uint64_t PRIME4 = 9650029242287828579ULL;
+static const uint64_t PRIME5 = 2870177450012600261ULL;
+
+NS_INLINE uint64_t rotl(uint64_t x, int r)
+{
+  return ((x << r) | (x >> (64 - r)));
+}
+
+NS_INLINE uint64_t mix1(const uint64_t h, const uint64_t prime, int rshift)
+{
+  return (h ^ (h >> rshift)) * prime;
+}
+
+NS_INLINE uint64_t mix2(const uint64_t p, const uint64_t v)
+{
+  return rotl(v + p * PRIME2, 31) * PRIME1;
+}
+
+NS_INLINE uint64_t mix3(const uint64_t h, const uint64_t v)
+{
+  return (h ^ mix2(v, 0)) * PRIME1 + PRIME4;
+}
+
+NS_INLINE uint32_t endian32(const char *v)
+{
+  return (uint32_t)((uint8_t)(v[0])) | ((uint32_t)((uint8_t)(v[1])) << 8)
+  | ((uint32_t)((uint8_t)(v[2])) << 16) | ((uint32_t)((uint8_t)(v[3])) << 24);
+}
+
+NS_INLINE uint64_t endian64(const char *v)
+{
+  return (uint64_t)((uint8_t)(v[0])) | ((uint64_t)((uint8_t)(v[1])) << 8)
+  | ((uint64_t)((uint8_t)(v[2])) << 16) | ((uint64_t)((uint8_t)(v[3])) << 24)
+  | ((uint64_t)((uint8_t)(v[4])) << 32) | ((uint64_t)((uint8_t)(v[5])) << 40)
+  | ((uint64_t)((uint8_t)(v[6])) << 48) | ((uint64_t)((uint8_t)(v[7])) << 56);
+}
+
+NS_INLINE uint64_t fetch64(const char *p, const uint64_t v)
+{
+  return mix2(endian64(p), v);
+}
+
+NS_INLINE uint64_t fetch32(const char *p)
+{
+  return (uint64_t)(endian32(p)) * PRIME1;
+}
+
+NS_INLINE uint64_t fetch8(const char *p)
+{
+  return (uint8_t)(*p) * PRIME5;
+}
+
+NS_INLINE uint64_t finalize(const uint64_t h, const char *p, uint64_t len)
+{
+  return (len >= 8) ? (finalize(rotl(h ^ fetch64(p, 0), 27) * PRIME1 + PRIME4, p + 8, len - 8))
+  : ((len >= 4) ? (finalize(rotl(h ^ fetch32(p), 23) * PRIME2 + PRIME3, p + 4, len - 4))
+      : ((len > 0) ? (finalize(rotl(h ^ fetch8(p), 11) * PRIME1, p + 1, len - 1))
+          : (mix1(mix1(mix1(h, PRIME2, 33), PRIME3, 29), 1, 32))));
+}
+
+NS_INLINE uint64_t h32bytes_compute(const char *p, uint64_t len, const uint64_t v1, const uint64_t v2, const uint64_t v3, const uint64_t v4)
+{
+  return (len >= 32) ? h32bytes_compute(p + 32, len - 32, fetch64(p, v1), fetch64(p + 8, v2), fetch64(p + 16, v3), fetch64(p + 24, v4))
+  : mix3(mix3(mix3(mix3(rotl(v1, 1) + rotl(v2, 7) + rotl(v3, 12) + rotl(v4, 18), v1), v2), v3), v4);
+}
+
+NS_INLINE uint64_t h32bytes(const char *p, uint64_t len, const uint64_t seed)
+{
+  return h32bytes_compute(p, len, seed + PRIME1 + PRIME2, seed + PRIME2, seed, seed - PRIME1);
+}
+
+NS_INLINE uint64_t FBxxHash64(const char *p, uint64_t len, uint64_t seed)
+{
+  return finalize((len >= 32 ? h32bytes(p, len, seed) : seed + PRIME5) + len, p + (len & ~0x1F), len & 0x1F);
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+NS_ASSUME_NONNULL_END