A quick & dirty port of translations_from_po() in https://github.com/uroni/urbackup_backend/blob/next/urbackupserver/www/translation_helper.py

Program.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using SecondLanguage;

namespace ConsoleApplication1
{
    public static class Program
    {
        private const string RootDirectory = @"C:\Temp\UrBackup";
        private const string TranslationDirectory = @"translations\urbackup.webinterface";
        private const string JSFilePath = @"js\translation.js";

        private static readonly IDictionary<string, string> LanguageMap = new Dictionary<string, string>()
        {
            { "fa_IR", "fa" }
        };

        public static void Main(string[] args)
        {
            Console.WindowWidth = 120;

            using (var writer = new StreamWriter(Path.Combine(RootDirectory, JSFilePath), false, Encoding.UTF8))
            {
                writer.Write("if(!window.translations) translations=new Object();\n");

                foreach (var file in Directory.EnumerateFiles(Path.Combine(RootDirectory, TranslationDirectory), "*.po"))
                {
                    var lang = Regex.Match(Path.GetFileName(file), @"(?<lang>[A-Za-z_]*).*\.po").Groups["lang"].ToString();
                    if (!string.IsNullOrEmpty(lang))
                    {
                        var po = new GettextPOTranslation();
                        po.Load(file);
                        var keys = po.GetGettextKeys().Where(x => !string.IsNullOrEmpty(x.Key.ID) && !string.IsNullOrEmpty(x.Value.FirstOrDefault())).ToList();
                        if (keys.Any(x => !string.IsNullOrEmpty(x.Value.First())))
                        {
                            Console.WriteLine($"{lang}:\t{keys.Count} keys \t{file}");

                            writer.WriteLine(
                                $"translations.{(LanguageMap.ContainsKey(lang) ? LanguageMap[lang] : lang)} = {{\n"
                                + string.Join(
                                    ",\n",
                                    keys.Select(x => $@"""{x.Key.ID.Escape()}"": ""{po.GetString(x.Key.ID).Escape()}"""))
                                + "\n}");
                        }
                    }                    
                }
            }

            Console.WriteLine("\nPress any key to exit.");
            Console.ReadKey();
        }

        private static string Escape(this string s) => s.Replace(@"""", @"\""").Replace("\n", @"\n");
    }
}