index.js

var finder = require('find-in-files');
var fs = require('fs-extra');
let languages = ["de","en","es-mx","es","fr","it","ja","ko","pl","pt-br","ru","zh-chs","zh-cht"];


async function findStrings(){
  let results = await finder.find(/TranslatedTextWidget\(\s*?["'](.*?)["'].*?[;,)]/, './../lib', '.dart$');
  return parseResults(results);
}

function parseResults(results){
  let foundStrings = [];
  for (let i in results) {
    let result = results[i];
    parseResult(i, result, foundStrings);
  }
  return foundStrings;
}

function parseResult(key, result, foundStrings) {
  for (let i in result.matches) {
    if(!result.matches[i]) continue;
    let match = result.matches[i];
    let regexpSingleQuote = /TranslatedTextWidget\(.*?['](.*?)[']/s;
    let regexpDoubleQuote = /TranslatedTextWidget\(.*?["](.*?)["]/s;
    let regMatch = regexpSingleQuote.exec(match) || regexpDoubleQuote.exec(match);
    let matchResult = regMatch[1];
    foundStrings.push(matchResult);
  }
}

async function copyOriginalLanguageFiles(){
  for(var i in languages){
    let language = languages[i];
    let exists = await fs.exists(`./languages/${language}.json`);  
    if(!exists){
      await fs.copy(`../assets/i18n/${language}.json`, `./languages/${language}.json`);
    }
  }
}

async function updateLanguageFiles(strings) {
  let missingStrings = {};
  for(var i in languages){
    await updateLanguageFile(languages[i], strings, missingStrings);
  }
  return missingStrings;
}

async function updateLanguageFile(language, strings, missingStrings){
  let contents = await fs.readJson(`./languages/${language}.json`);
  for(var i in strings){
    let str = strings[i];
    let placeholder = `#####${str}`;
    if(!contents[str]){
      if(!missingStrings[language]) missingStrings[language] = [];
      missingStrings[language].push(str);
    }
    if(!contents[str] && !contents[placeholder]){
      contents[placeholder] = "missing_translation";
    }
  }
  await fs.writeJson(`./languages/${language}.json`, contents, {spaces:2});
}

function printResults(result){
  let divider = '--------------------------------------------------------------------------------';
  for(let language in result){
    let results = result[language];
    console.log(divider);
    console.log(language);
    console.log(`Missing ${results.length} translations:`)
    for(var i in results){
      console.log(`   - ${results[i]}`)
    }
    console.log(divider);
    console.log('');
  }
}

async function run(){
  await fs.mkdirp('./languages');
  copyOriginalLanguageFiles();
  let strings = await findStrings();
  let result = await updateLanguageFiles(strings);
  printResults(result);
}

run();