Simple Translator in JS

translator.js

const FR_FR_TRANSLATIONS = require("./fr-FR.json");
const EN_US_TRANSLATIONS = require("./en-US.json");

class Translator {
  constructor() {
    this.setLanguage("en-US");
  }

  setLanguage = (newLang) => {
    switch (newLang) {
      case "fr-FR":
        this.language = "fr-FR";
        this.translations = FR_FR_TRANSLATIONS;
        break;
      case "en-US":
      default:
        this.language = "en-US";
        this.translations = EN_US_TRANSLATIONS;
    }
  };

  _insertArguments = (text, arg) => {
    if (!arg) {
      return text;
    }

    return text.replace(/\$\-/g, arg);
  };

  get = (text, arg) => {
    const currentTranslation = this.translations[text.toUpperCase()];

    if (!currentTranslation) {
      return text;
    }

    if (typeof currentTranslation === "string") {
      return this._insertArguments(currentTranslation, arg);
    }

    if (arg === undefined || arg === null) {
      if (!currentTranslation.null) {
        throw new Error(`Cannot find null translation for ${text}`);
      }

      return currentTranslation.null;
    }

    if (currentTranslation[String(arg)]) {
      return this._insertArguments(currentTranslation[String(arg)], arg);
    }

    if (!currentTranslation.N) {
      throw new Error(`Cannot find N translation for ${text}`);
    }

    return this._insertArguments(currentTranslation.N, arg);
  };
}

const translator = new Translator();

export default translator;