diff --git a/.changeset/allow-valid-locale-codes.md b/.changeset/allow-valid-locale-codes.md
new file mode 100644
index 000000000..b3131f2ee
--- /dev/null
+++ b/.changeset/allow-valid-locale-codes.md
@@ -0,0 +1,5 @@
+---
+"@lingo.dev/_spec": minor
+---
+
+Allow any valid ISO locale code in validation instead of hardcoded list. Validation now accepts any locale conforming to ISO 639-1, ISO 15924, ISO 3166-1, and UN M.49 standards.
diff --git a/CLAUDE.md b/CLAUDE.md
index e195030c5..cf51f307f 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -10,4 +10,10 @@
 
 ## Testing
 
-- When you add tests - make sure they pass
\ No newline at end of file
+- When you add tests - make sure they pass
+
+## Changesets
+
+- Every PR must include a changeset
+- Create changeset: `pnpm new` from repo root
+- For changes that don't need a release (e.g., README updates): `pnpm new:empty`
\ No newline at end of file
diff --git a/packages/spec/package.json b/packages/spec/package.json
index c572975aa..528227aa0 100644
--- a/packages/spec/package.json
+++ b/packages/spec/package.json
@@ -25,6 +25,7 @@
   "author": "",
   "license": "Apache-2.0",
   "dependencies": {
+    "@lingo.dev/_locales": "workspace:*",
     "zod": "^3.25.76",
     "zod-to-json-schema": "^3.24.5"
   },
diff --git a/packages/spec/src/locales.ts b/packages/spec/src/locales.ts
index da954e416..dac57f1b5 100644
--- a/packages/spec/src/locales.ts
+++ b/packages/spec/src/locales.ts
@@ -1,4 +1,5 @@
 import Z from "zod";
+import { isValidLocale } from "@lingo.dev/_locales";
 
 const localeMap = {
   // Urdu (Pakistan)
@@ -246,7 +247,11 @@ export const localeCodes = [
 ] as LocaleCode[];
 
 export const localeCodeSchema = Z.string().refine(
-  (value) => localeCodes.includes(value as any),
+  (value) => {
+    // Normalize locale before validation
+    const normalized = normalizeLocale(value);
+    return isValidLocale(normalized);
+  },
   {
     message: "Invalid locale code",
   },
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 1c506460e..0feceaef3 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -928,6 +928,9 @@ importers:
 
   packages/spec:
     dependencies:
+      '@lingo.dev/_locales':
+        specifier: workspace:*
+        version: link:../locales
       zod:
         specifier: ^3.25.76
         version: 3.25.76