diff --git a/apps/scratch-frame/src/ScratchEditor.jsx b/apps/scratch-frame/src/ScratchEditor.jsx
index 4c159827c..2a120e52a 100644
--- a/apps/scratch-frame/src/ScratchEditor.jsx
+++ b/apps/scratch-frame/src/ScratchEditor.jsx
@@ -40,6 +40,7 @@ const ScratchEditor = ({
   locale,
   apiUrl,
   accessToken: initialAccessToken,
+  projectLocale,
 }) => {
   const [accessToken, setAccessToken] = useState(initialAccessToken);
 
@@ -89,6 +90,10 @@ const ScratchEditor = ({
       basePath={`${import.meta.env.REACT_APP_SCRATCH_FRAME_URL}/scratch-gui/`}
       onStorageInit={(storage) => {
         scratchFetchApiRef.current = storage.scratchFetch;
+        scratchFetchApiRef.current.setMetadata(
+          "X-Project-Locale",
+          projectLocale,
+        );
         if (accessToken) {
           scratchFetchApiRef.current.setMetadata("Authorization", accessToken);
         }
diff --git a/apps/scratch-frame/src/ScratchEditor.test.jsx b/apps/scratch-frame/src/ScratchEditor.test.jsx
index 6b2483fd0..185e7a1ed 100644
--- a/apps/scratch-frame/src/ScratchEditor.test.jsx
+++ b/apps/scratch-frame/src/ScratchEditor.test.jsx
@@ -102,6 +102,32 @@ describe("ScratchEditor", () => {
     );
   });
 
+  test("sends the project locale with scratch requests after storage init", () => {
+    render(
+      <ScratchEditor
+        projectId="project-123"
+        locale="fr"
+        apiUrl="https://api.example.com"
+        accessToken="token-123"
+        projectLocale="fr-FR"
+      />,
+    );
+
+    const scratchGuiProps = mockWrappedScratchGui.mock.calls[0][0];
+    const scratchStorage = {
+      scratchFetch: {
+        setMetadata: vi.fn(),
+      },
+    };
+
+    scratchGuiProps.onStorageInit(scratchStorage);
+
+    expect(scratchStorage.scratchFetch.setMetadata).toHaveBeenCalledWith(
+      "X-Project-Locale",
+      "fr-FR",
+    );
+  });
+
   test("updates scratchFetch metadata when scratch-gui-update-token message is received", () => {
     render(
       <ScratchEditor
diff --git a/apps/scratch-frame/src/scratch.jsx b/apps/scratch-frame/src/scratch.jsx
index da35bfd63..8ee4a10d2 100644
--- a/apps/scratch-frame/src/scratch.jsx
+++ b/apps/scratch-frame/src/scratch.jsx
@@ -70,6 +70,7 @@ if (!projectId) {
           locale={locale}
           apiUrl={apiUrl}
           accessToken={accessToken}
+          projectLocale={raspberryPiLocale}
         />
       </>,
     );
diff --git a/apps/scratch-frame/src/scratch.test.js b/apps/scratch-frame/src/scratch.test.js
index bd325320a..21f8f34a3 100644
--- a/apps/scratch-frame/src/scratch.test.js
+++ b/apps/scratch-frame/src/scratch.test.js
@@ -149,7 +149,9 @@ describe("scratch handshake retries", () => {
       );
 
       await loadScratchModule();
-      expect(mountScratchEditor().locale).toBe(expected);
+      const scratchEditorProps = mountScratchEditor();
+      expect(scratchEditorProps.locale).toBe(expected);
+      expect(scratchEditorProps.projectLocale).toBe(locale);
     },
   );
 
diff --git a/cypress/e2e/spec-scratch.cy.js b/cypress/e2e/spec-scratch.cy.js
index 8c4c14f90..4d16536e7 100644
--- a/cypress/e2e/spec-scratch.cy.js
+++ b/cypress/e2e/spec-scratch.cy.js
@@ -10,6 +10,7 @@ import {
 const origin = "http://localhost:3011/web-component.html";
 const scratchFrameOrigin = Cypress.env("REACT_APP_SCRATCH_FRAME_URL");
 const authKey = "oidc.user:https://auth-v1.raspberrypi.org:editor-api";
+const scratchProjectsApiMatcher = "**/api/scratch/projects/**";
 const user = {
   access_token: "dummy-access-token",
   profile: {
@@ -107,6 +108,18 @@ describe("Scratch locale", () => {
     });
   });
 
+  it("sets a header with the project locale", () => {
+    cy.intercept("GET", scratchProjectsApiMatcher).as("scratchProjectRequest");
+
+    cy.visit(scratchProjectURL({ locale: "fr-FR" }));
+
+    cy.wait("@scratchProjectRequest")
+      .its("request.headers")
+      .then((headers) => {
+        expect(headers["x-project-locale"]).to.equal("fr-FR");
+      });
+  });
+
   it("falls back to English when Scratch does not support the locale", () => {
     cy.visit(scratchProjectURL({ locale: "vls-BE" }));
 
@@ -220,7 +233,6 @@ describe("Scratch save integration", () => {
 });
 
 describe("Scratch Authorization header", () => {
-  const scratchProjectsApiMatcher = "**/api/scratch/projects/**";
   const remixApiMatcher = "**/api/projects/*/remix";
 
   it("includes Authorization header when authKey and access token are present in localStorage", () => {