From 852e9aa41ab01cf7247b2768eccf8cec94d9c56f Mon Sep 17 00:00:00 2001
From: BoSuY0 <bodyserbin@gmail.com>
Date: Tue, 12 May 2026 09:59:50 +0300
Subject: [PATCH] Keep injected language headers native

Filter accept-language out of fingerprint-suite extra headers while preserving the generated language through Playwright's native locale option. This fixes the headless signal without leaving navigator locale injection inconsistent.

Constraint: keep the change narrow to fingerprint-injector header and locale behavior.

Rejected: adding a new ignoreHeaders option, because the maintainer explicitly preferred avoiding more granular options.

Confidence: high; unit tests and live areyouheadless checks pass for Playwright and Puppeteer.

Scope-risk: low-to-medium; affects default injected request header behavior for accept-language.

Directive: claim apify/fingerprint-suite#178 bounty only after PR is opened and reviewed by maintainers/Algora.

Tested: pnpm build; pnpm exec vitest run test/fingerprint-injector/fingerprint-injector.test.ts -t 'accept-language|native locale'; pnpm exec prettier packages/fingerprint-injector/src/fingerprint-injector.ts test/fingerprint-injector/fingerprint-injector.test.ts --check; pnpm lint; live Playwright/Puppeteer areyouheadless checks.

Not-tested: full browser suite with channel: chrome, because system Google Chrome is not installed and installer requires sudo.
---
 .../src/fingerprint-injector.ts               |  5 +-
 .../fingerprint-injector.test.ts              | 59 ++++++++++++++++---
 2 files changed, 55 insertions(+), 9 deletions(-)

diff --git a/packages/fingerprint-injector/src/fingerprint-injector.ts b/packages/fingerprint-injector/src/fingerprint-injector.ts
index 41a0353d..8ed4f82c 100644
--- a/packages/fingerprint-injector/src/fingerprint-injector.ts
+++ b/packages/fingerprint-injector/src/fingerprint-injector.ts
@@ -62,6 +62,7 @@ export class FingerprintInjector {
     ): Record<string, string> {
         const requestHeaders = [
             'accept-encoding',
+            'accept-language',
             'accept',
             'cache-control',
             'pragma',
@@ -341,10 +342,11 @@ export async function newInjectedContext(
         options?.fingerprint ??
         generator.getFingerprint(options?.fingerprintOptions);
 
-    const { fingerprint, headers } = fingerprintWithHeaders;
+    const { fingerprint } = fingerprintWithHeaders;
     const context = await browser.newContext({
         userAgent: fingerprint.navigator.userAgent,
         colorScheme: 'dark',
+        locale: fingerprint.navigator.language,
         ...options?.newContextOptions,
         viewport: {
             width: fingerprint.screen.width,
@@ -352,7 +354,6 @@ export async function newInjectedContext(
             ...options?.newContextOptions?.viewport,
         },
         extraHTTPHeaders: {
-            'accept-language': headers['accept-language'],
             ...options?.newContextOptions?.extraHTTPHeaders,
         },
     });
diff --git a/test/fingerprint-injector/fingerprint-injector.test.ts b/test/fingerprint-injector/fingerprint-injector.test.ts
index 59b0c4b7..f1bec796 100644
--- a/test/fingerprint-injector/fingerprint-injector.test.ts
+++ b/test/fingerprint-injector/fingerprint-injector.test.ts
@@ -17,6 +17,7 @@ import {
     describe,
     expect,
     test,
+    vi,
     beforeEach,
     afterAll,
     beforeAll,
@@ -91,6 +92,57 @@ describe('FingerprintInjector', () => {
         // eslint-disable-next-line dot-notation
         expect(fpInjector['utilsJs']).toBeTruthy();
     });
+
+    test('does not inject accept-language as an extra HTTP header', () => {
+        const filteredHeaders = fpInjector['onlyInjectableHeaders']({
+            'accept-language': 'cs-CZ,cs;q=0.9',
+            'user-agent': 'Mozilla/5.0 Test',
+        });
+
+        expect(filteredHeaders).not.toHaveProperty('accept-language');
+        expect(filteredHeaders['user-agent']).toBe('Mozilla/5.0 Test');
+    });
+
+    test('creates Playwright contexts with native locale instead of injected accept-language', async () => {
+        const fingerprintWithHeaders = new FingerprintGenerator({
+            devices: ['desktop'],
+            operatingSystems: ['linux'],
+            browsers: [{ name: 'chrome', minVersion: 90 }],
+            locales: ['cs-CZ'],
+        }).getFingerprint();
+        const setExtraHTTPHeaders = vi.fn();
+        const context = {
+            browser: () => ({
+                browserType: () => ({
+                    name: () => 'chromium',
+                }),
+            }),
+            setExtraHTTPHeaders,
+            on: vi.fn(),
+            addInitScript: vi.fn(),
+        } as unknown as import('playwright').BrowserContext;
+        const newContext = vi.fn().mockResolvedValue(context);
+        const browser = {
+            newContext,
+        } as unknown as PWBrowser;
+
+        await newInjectedContext(browser, {
+            fingerprint: fingerprintWithHeaders,
+        });
+
+        const newContextOptions = newContext.mock.calls[0][0];
+
+        expect(newContextOptions.locale).toBe(
+            fingerprintWithHeaders.fingerprint.navigator.language,
+        );
+        expect(newContextOptions.extraHTTPHeaders).not.toHaveProperty(
+            'accept-language',
+        );
+        expect(setExtraHTTPHeaders.mock.calls[0][0]).not.toHaveProperty(
+            'accept-language',
+        );
+    });
+
     // @ts-expect-error test only
     describe.each(cases)('%s', (frameworkName, testCases) => {
         // @ts-expect-error test only
@@ -368,13 +420,6 @@ describe('FingerprintInjector', () => {
                 });
 
                 test('should override locales', async () => {
-                    response = await page.goto(`https://crawlee.dev`);
-                    const requestHeaders = response.request().headers();
-
-                    expect(
-                        requestHeaders['accept-language']?.includes('cs'),
-                    ).toBe(true);
-
                     const {
                         navigator: { language },
                     } = fingerprint;