next-i18next.config.js

const path = require('path');
const isProd = process.env.NODE_ENV === 'production';
const isUploadingTranslations = process.env.UPLOAD_TRANSLATIONS === '1';
const uploadHistory = new Map();

module.exports = {
  i18n: {
    serializeConfig: isProd,
    defaultLocale: 'en',
    locales: ['en', 'zh_hans'],
    localePath: path.resolve('./public/locales'),
    nsSeparator: false,
    keySeparator: false,
    saveMissing: isUploadingTranslations,
    serializeConfig: false,
    returnEmptyString: false,
    missingKeyHandler: isUploadingTranslations
      ? (_lngs, _ns, key, fallbackValue) => {
          const localizationEndpoint =
            'https://api.simplelocalize.io/api/v1/translations';
          const localizationApiKey =
            '5cE94de8403d5C076833BE98aC44FE7314e3e52f9EBFC86DF55e3fCa69A6B26A';

          const data = {
            key,
            language: 'en', // Default language
            text: fallbackValue,
          };

          if (!uploadHistory.has(key)) {
            fetch(localizationEndpoint, {
              method: 'POST',
              headers: {
                'Content-Type': 'application/json',
                'X-SimpleLocalize-Token': localizationApiKey,
              },
              body: JSON.stringify({ content: [data] }),
            })
              .then(() => {
                uploadHistory.set(key, true);
                console.info('Uploaded missing translation key', data);
              })
              .catch((error) => {
                console.error('Error trying to upload missing key', error);
              });
          }
        }
      : undefined,
  },
};