Copy.js

class Copy {
  static language = 'en';
  static languageMap = {
    en: { Hello: 'Hello' },
    sp: { Hello: 'Hola' },
  };

  set language(language) {
    Copy.language = language;
  }

  get language() {
    return Copy.language;
  }

  write(text = '') {
    const { language, languageMap } = Copy;
    const hasMatch = languageMap[language] && languageMap[language][text];
    const words = hasMatch ? languageMap[language][text] : text;
    return words;
  }
}

// Make Copy a singleton
const instance = new Copy();
Object.freeze(instance);
export default instance;

// Somewhere else in your code
import React from 'react';
import Copy from './Copy';

// You can set this once in a root component and it will stay the same everywhere because it is a singleton
Copy.language = 'sp';

export default class App extends React.PureComponent {
  render() {
    // outputs "Hola World!"
    return (
      <h1>{Copy.write('Hello')} World!</h1>
    );
  }
}