feat: add language selector component to header

src/index.scss

@@ -7,6 +7,7 @@ $rounded-pill: 50rem  !default;
 
 @import './Menu/menu.scss';
 @import './studio-header/StudioHeader.scss';
+@import './language-selector/LanguageSelector.scss';
 
 .dropdown-item a {
   text-decoration: none;

src/language-selector/LanguageSelector.jsx

@@ -0,0 +1,99 @@
+import PropTypes from 'prop-types';
+import React, { useContext, useState } from 'react';
+
+import { changeUserSessionLanguage, getPrimaryLanguageSubtag, injectIntl } from '@edx/frontend-platform/i18n';
+import { getLocale } from '@edx/frontend-platform/i18n/lib';
+import { AppContext } from '@edx/frontend-platform/react';
+import { Dropdown } from '@openedx/paragon';
+import { Language } from '@openedx/paragon/icons';
+
+/**
+ * Gets the localized display name of a language in its own language.
+ *
+ * @function getDisplayName
+ * @param {string} locale - The locale code (e.g., 'en', 'es', 'ar')
+ * @returns {string} The capitalized display name of the language in its native form
+ * @example
+ */
+const getDisplayName = (locale) => {
+  const langName = new Intl.DisplayNames([locale], { type: 'language', languageDisplay: 'standard' }).of(locale);
+  return langName.charAt(0).toUpperCase() + langName.slice(1);
+};
+
+/**
+ * Language Selector component that displays a dropdown allowing users to change the site language.
+ *
+ * The component is responsive and adapts to different screen sizes:
+ * - On large screens: Shows the full language name (e.g., "English")
+ * - On medium screens: Shows the language code (e.g., "EN")
+ * - On small screens: Shows only the language icon
+ *
+ * @component
+ * @param {Object} props - Component props
+ * @param {string} [props.className=''] - Additional CSS class names to apply to the component
+ * @returns {React.Element|null} The rendered component or null if disabled or no supported languages
+ *
+ * @requires config.SITE_SUPPORTED_LANGUAGES - Must be a non-empty array of locale codes
+ * @requires config.LANGUAGE_PREFERENCE_COOKIE_NAME - Cookie name for storing language preference
+ */
+const LanguageSelector = ({ className }) => {
+  const { config } = useContext(AppContext);
+
+  const languageOptions = config.SITE_SUPPORTED_LANGUAGES;
+  const [currentLocale, setCurrentLocale] = useState(getLocale());
+
+  /**
+   * Handles the selection of a language from the dropdown.
+   * Only triggers language change if the selected language is different from the current one.
+   *
+   * @param {string} selectedLocale - The locale code selected by the user
+   */
+  const handleSelect = (selectedLocale) => {
+    if (currentLocale !== selectedLocale) {
+      changeUserSessionLanguage(selectedLocale);
+      setCurrentLocale(selectedLocale);
+    }
+  };
+
+  const currentLangCode = getPrimaryLanguageSubtag(currentLocale).toUpperCase();
+  const currentlangDisplayName = getDisplayName(currentLocale);
+
+  // Don't render the component if there are no language options
+  if (!Array.isArray(languageOptions)
+    || languageOptions.length === 0) {
+    return null;
+  }
+
+  return (
+    <div className={`${className} language-selector`} id="language-selector">
+      <Dropdown onSelect={handleSelect}>
+        <Dropdown.Toggle
+          id="lang-selector-dropdown"
+          iconBefore={Language}
+          variant="outline-primary"
+          size="sm"
+        >
+          <span className="lang-label-medium">{currentLangCode}</span>
+          <span className="lang-label-large">{currentlangDisplayName}</span>
+        </Dropdown.Toggle>
+        <Dropdown.Menu>
+          {languageOptions.map((locale) => (
+            <Dropdown.Item key={`lang-selector-${locale}`} eventKey={locale}>
+              {getDisplayName(locale)}
+            </Dropdown.Item>
+          ))}
+        </Dropdown.Menu>
+      </Dropdown>
+    </div>
+  );
+};
+
+LanguageSelector.propTypes = {
+  className: PropTypes.string,
+};
+
+LanguageSelector.defaultProps = {
+  className: '',
+};
+
+export default injectIntl(LanguageSelector);

src/language-selector/LanguageSelector.scss

@@ -0,0 +1,22 @@
+.language-selector {
+  padding: .75rem;
+
+  .dropdown-toggle {
+    .lang-label-medium,
+    .lang-label-large {
+      display: none;
+    }
+
+    @media (min-width: 576px) and (max-width: 767px) {
+      .lang-label-medium {
+        display: inline;
+      }
+    }
+
+    @media (min-width: 768px) {
+      .lang-label-large {
+        display: inline;
+      }
+    }
+  }
+}

src/language-selector/LanguageSelector.test.jsx

@@ -0,0 +1,131 @@
+import React from 'react';
+import { mergeConfig } from '@edx/frontend-platform';
+import { getLocale } from '@edx/frontend-platform/i18n/lib';
+import { changeUserSessionLanguage } from '@edx/frontend-platform/i18n';
+import {
+  act, fireEvent, initializeMockApp, render, screen,
+} from '../setupTest';
+import LanguageSelector from './LanguageSelector';
+
+jest.mock('@edx/frontend-platform/i18n', () => ({
+  ...jest.requireActual('@edx/frontend-platform/i18n'),
+  changeUserSessionLanguage: jest.fn().mockResolvedValue({}),
+}));
+
+jest.mock('@edx/frontend-platform/i18n/lib', () => ({
+  ...jest.requireActual('@edx/frontend-platform/i18n/lib'),
+  getLocale: jest.fn(),
+}));
+
+jest.mock('@openedx/paragon/icons', () => ({
+  Language: () => <div>LanguageIcon</div>,
+}));
+
+jest.mock('@openedx/paragon', () => ({
+  ...jest.requireActual('@openedx/paragon'),
+  useWindowSize: () => ({ width: global.innerWidth }),
+}));
+
+const LANGUAGE_PREFERENCE_COOKIE_NAME = 'language-preference';
+
+describe('LanguageSelector', () => {
+  let mockReload;
+
+  beforeEach(() => {
+    jest.clearAllMocks();
+
+    mergeConfig({
+      ENABLE_HEADER_LANG_SELECTOR: true,
+      LANGUAGE_PREFERENCE_COOKIE_NAME,
+      SITE_SUPPORTED_LANGUAGES: ['es', 'en'],
+    });
+
+    initializeMockApp();
+
+    mockReload = jest.fn();
+    Object.defineProperty(window, 'location', {
+      configurable: true,
+      writable: true,
+      value: { reload: mockReload },
+    });
+
+    global.innerWidth = 1200;
+  });
+
+  it('should not render when no supported languages are available', () => {
+    mergeConfig({
+      SITE_SUPPORTED_LANGUAGES: [],
+    });
+
+    const { container } = render(<LanguageSelector />);
+    // expect(container).toMatchSnapshot('no-supported-languages');
+    expect(container.querySelector('#language-selector')).toBeNull();
+  });
+
+  it('should change the language when different language is selected', async () => {
+    getLocale.mockReturnValue('en');
+
+    const { container } = render(<LanguageSelector />);
+    expect(container).toMatchSnapshot('before-language-change');
+
+    const langDropdown = screen.getByRole('button', { id: 'lang-selector-dropdown' });
+    fireEvent.click(langDropdown);
+
+    const spanishOption = screen.getByRole('button', { name: 'Español' });
+
+    await act(async () => {
+      fireEvent.click(spanishOption);
+    });
+
+    expect(container).toMatchSnapshot('after-language-change');
+    expect(changeUserSessionLanguage).toHaveBeenCalledWith('es');
+  });
+
+  it('should not change language if the same language is selected', async () => {
+    getLocale.mockReturnValue('en');
+
+    const { container } = render(<LanguageSelector />);
+    expect(container).toMatchSnapshot('before-same-language-selection');
+
+    const langDropdown = screen.getByRole('button', { id: 'lang-selector-dropdown' });
+    fireEvent.click(langDropdown);
+
+    const englishOption = screen.getByRole('button', { name: 'English' });
+    await act(async () => {
+      fireEvent.click(englishOption);
+    });
+
+    expect(container).toMatchSnapshot('after-same-language-selection');
+    expect(changeUserSessionLanguage).not.toHaveBeenCalled();
+  });
+
+  it('should display full language name on large screens', () => {
+    getLocale.mockReturnValue('en');
+
+    global.innerWidth = 1200;
+    render(<LanguageSelector />);
+
+    const button = screen.getByRole('button', { id: 'lang-selector-dropdown' });
+    expect(button).toMatchSnapshot('large-screen-button');
+  });
+
+  it('should display language code on medium screens', () => {
+    getLocale.mockReturnValue('en');
+
+    global.innerWidth = 700;
+    render(<LanguageSelector />);
+
+    const button = screen.getByRole('button', { id: 'lang-selector-dropdown' });
+    expect(button).toMatchSnapshot('medium-screen-button');
+  });
+
+  it('should display only icon on small screens', () => {
+    getLocale.mockReturnValue('en');
+
+    global.innerWidth = 500;
+    render(<LanguageSelector />);
+
+    const button = screen.getByRole('button', { id: 'lang-selector-dropdown' });
+    expect(button).toMatchSnapshot('small-screen-button');
+  });
+});