Have you used localization (i18n)? How many languages are supported?

Yes, I have used localization (i18n) in several projects. Usually, 2 to 5 languages are supported, including Russian and English, with German and French sometimes added. To implement this, I used libraries such as i18next or react-intl, which allow dynamically changing the interface language and loading the corresponding translations.

Example of using i18next in React:

import { useTranslation } from 'react-i18next';

function MyComponent() {
  const { t, i18n } = useTranslation();

  const changeLanguage = (lng) => {
    i18n.changeLanguage(lng);
  };

  return (
    <div>
      <h1>{t('welcome_message')}</h1>
      <button onClick={() => changeLanguage('en')}>English</button>
      <button onClick={() => changeLanguage('ru')}>Russian</button>
    </div>
  );
}