diff --git a/.changeset/rude-penguins-live.md b/.changeset/rude-penguins-live.md
new file mode 100644
index 00000000..daf4ae9c
--- /dev/null
+++ b/.changeset/rude-penguins-live.md
@@ -0,0 +1,5 @@
+---
+"@rebilly/client-php": patch
+---
+
+fix(api-definitions): Add missing locale in Customer.yaml Rebilly/rebilly#8662
diff --git a/src/Model/Customer.php b/src/Model/Customer.php
index 8e1e29ed..b7e3cf84 100644
--- a/src/Model/Customer.php
+++ b/src/Model/Customer.php
@@ -89,6 +89,9 @@ public function __construct(array $data = [])
         if (array_key_exists('organizationId', $data)) {
             $this->setOrganizationId($data['organizationId']);
         }
+        if (array_key_exists('locale', $data)) {
+            $this->setLocale($data['locale']);
+        }
         if (array_key_exists('taxNumbers', $data)) {
             $this->setTaxNumbers($data['taxNumbers']);
         }
@@ -301,6 +304,18 @@ public function getOrganizationId(): ?string
         return $this->fields['organizationId'] ?? null;
     }
 
+    public function getLocale(): ?string
+    {
+        return $this->fields['locale'] ?? null;
+    }
+
+    public function setLocale(null|string $locale): static
+    {
+        $this->fields['locale'] = $locale;
+
+        return $this;
+    }
+
     /**
      * @return null|TaxNumber[]
      */
@@ -422,6 +437,9 @@ public function jsonSerialize(): array
         if (array_key_exists('organizationId', $this->fields)) {
             $data['organizationId'] = $this->fields['organizationId'];
         }
+        if (array_key_exists('locale', $this->fields)) {
+            $data['locale'] = $this->fields['locale'];
+        }
         if (array_key_exists('taxNumbers', $this->fields)) {
             $data['taxNumbers'] = $this->fields['taxNumbers'] !== null
                 ? array_map(