Map usage

index.js

const infoLanguage = [
  {language: 'Javascript', extension: '.js' },
  {language: 'Python', extension: '.py'},
  {language: 'PHP', extension: '.php'},
  {language: 'Java', extension: '.java'},
  {language: 'HTML', extension: '.html'},
  {language: 'CSS', extension: '.css'},
]

const languagesExtensions = new Map();

for (let language of infoLanguage) {
  languagesExtensions.set(language.language, language.extension);
}

const getExtensions = (language) => {
  let extension = languagesExtensions.get(language);
  if (extension === undefined) {
    return 'Não temos a extensão para essa linguagem! :(';
  }
  return extension;
}

console.log(getExtensions('Python')); // .py