feat(lang) add helper script for manual translations

It updates the main language file for a given locale from the canonical one and
sets the empty string on the missing keys. No longer used keys are discarded.

lang/readme.md

-Jitsi Meet Translation
-==========================
+# Jitsi Meet Translation
+
 Jitsi Meet uses [i18next](http://i18next.com) library for translation.
 i18next uses separate json files for each language.
 
 
-Translating Jitsi Meet
-======================
+## Translating Jitsi Meet
+
 The translation of Jitsi Meet is handled editing manually the language files.
 
-Development
-===========
+You can use the `update-translation.js` script as follows to help you with that:
+
+```js
+cd lang
+node update-translation.js main-es.json
+```
+
+That will cause the `main-es.json` file to be updated with all the missing keys set as empty
+strings. All that's missing is for you to fill in the blanks!
+
+## Development
+
 If you want to add new functionality for Jitsi Meet and you have texts that need to be translated you must add key and value in main.json file in English for each translatable text.
 Than you can use the key to get the translated text for the current language.
 
 For the available values of ``options`` parameter for the above methods of translation module see [i18next documentation](http://i18next.com/pages/doc_features).
 
 **Note:** It is useful to add attributes in the HTML for persistent HTML elements because when the language is changed the text will be automatically translated.
-
-
-
-

lang/update-translation.js

+/* eslint-disable */
+
+const fs = require('fs');
+const process = require('process');
+const traverse = require('traverse');
+const mainLang = require('./main.json');
+
+const [ targetLangFile ] = process.argv.slice(-1);
+
+if (!targetLangFile) {
+    console.log('No target language file specified');
+    process.exit(1);
+}
+
+const targetLang = require(`./${targetLangFile}`);
+
+const paths = traverse(mainLang).reduce(function(acc, item) {
+    if (this.isLeaf) {
+        acc.push(this.path);
+    }
+
+    return acc;
+}, []);
+
+const result = {};
+
+for (const path of paths) {
+    if (traverse(targetLang).has(path)) {
+        traverse(result).set(path, traverse(targetLang).get(path));
+    } else {
+        //console.log(`${path.join('.')} is missing`);
+        traverse(result).set(path, '');
+    }
+}
+
+const data = JSON.stringify(result, undefined, 4);
+
+fs.writeFileSync(`./${targetLangFile}`, data);

package-lock.json

       "integrity": "sha512-yaOH/Pk/VEhBWWTlhI+qXxDFXlejDGcQipMlyxda9nthulaxLZUNcUqFxokp0vcYnvteJln5FNQDRrxj3YcbVw==",
       "dev": true
     },
+    "traverse": {
+      "version": "0.6.6",
+      "resolved": "https://registry.npmjs.org/traverse/-/traverse-0.6.6.tgz",
+      "integrity": "sha1-y99WD9e5r2MlAv7UD5GMFX6pcTc=",
+      "dev": true
+    },
     "trim-right": {
       "version": "1.0.1",
       "resolved": "https://registry.npmjs.org/trim-right/-/trim-right-1.0.1.tgz",

package.json

     "sass": "1.26.8",
     "string-replace-loader": "2.1.1",
     "style-loader": "0.19.0",
+    "traverse": "0.6.6",
     "unorm": "1.6.0",
     "webpack": "4.43.0",
     "webpack-bundle-analyzer": "3.4.1",