How to build a wordlist

So now I want to make Estonian wordlist ~about 20m unique words in lowercase. To get input for wordlist, corpus of Estonian can be used. Corpus files are in Text Encoding Initiative (TEI) format. I tried using regex to find the words.

This is what I made: it's inefficient, mcv is all messed up, it brakes if hashset of words can't fit in memory, it's not aware of inputs encoding - so probably letters like š make problems, it does not show estimated completion time, some controls have default names and some don't, it does not use multitasking (not sure if it should), it uses some weird fixes and lots of locking interface so that it would appear not 'frozen'. At least its so short, that you hardly notice there are no comments.

Upside is, that it can almost read words without many mistakes, from .tei, .txt, .csv, smgl, xhtml or any a like format inputs.

Now you know what I want to do, how I have tried doing it (with what problems), and again I'm just trying to find out how to do it (with minimal manual labor).

Image example:

Code example & Gui:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;
using System.IO;
using System.Text.RegularExpressions;

namespace Reader
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }


        private void listView1_DragEnter(object sender, DragEventArgs e)
        {
            if (e.Data.GetDataPresent(DataFormats.FileDrop, false) == true)
            {
                e.Effect = DragDropEffects.All;
            }  
        }

        private void listView1_DragDrop(object sender, DragEventArgs e)
        {
            setguiLock(true);
            this.loading.Visible = true;
            ignorechecking = true;
            string[] files = (string[])e.Data.GetData(DataFormats.FileDrop, false);
            Dictionary<String, ListViewGroup> listviewgroups = new Dictionary<string,ListViewGroup>();

            int filenamesi = 0;

            foreach (string file in files)
            {
                progresslabel.Text = string.Format("Progress: \t[ {0} / {1} ]", filenamesi++, files.Length);
                Application.DoEvents();
               if (File.Exists(file))
                {
                    FileInfo ff = new System.IO.FileInfo(file);
                    if (!listviewgroups.ContainsKey(ff.DirectoryName))
                    {
                        listviewgroups.Add(ff.DirectoryName, new ListViewGroup(ff.DirectoryName, HorizontalAlignment.Left));
                        listView1.Groups.Add(listviewgroups[ff.DirectoryName]);
                    }
                    ListViewItem item = new ListViewItem(ff.Name);
                    listviewgroups[ff.DirectoryName].Items.Add(item);
                    item.Checked = true;

                    item.SubItems.Add("" +((int)ff.Length/1024)+" KB");

                  //  item.Group.Header = ff.DirectoryName;
                  //  listviewgroups[ff.DirectoryName].Items.Add(item);
                    listView1.Items.Add(item);
               }
            }
            setguiLock(false);
            ignorechecking = false;
            this.loading.Visible = false;
            updatechecked();
        }

        private void listView1_ItemChecked(object sender, ItemCheckedEventArgs e)
        {
            updatechecked();
        }
        private bool ignorechecking = false;
        private void updatechecked(){
            if (ignorechecking)
                return;
            long size = 0;
            int count = 0;
            foreach (ListViewItem item in this.listView1.Items)
            {
                if (item.Checked)
                {
                    count++;
                    size += Int32.Parse(item.SubItems[1].Text.Split(" ".ToArray())[0]); 
                }
            }
            this.text1.Text = ""+count;
            this.text2.Text = ""+size + " KB";
        }
        private void putHashset(HashSet<string> d, string filename)
        {
            StringBuilder sb = new StringBuilder();
            foreach (string key in d) 
                sb.Append(key).Append("\n");

            File.WriteAllText(filename, sb.ToString());
        }
        private HashSet<string> getHashset(string filename)
        {
            return new HashSet<string>(new Regex("\\n+").Split(File.ReadAllText(filename)));
        }

        private void removefilefromlistview(string fullfilename) {
            foreach (ListViewItem item in this.listView1.Items)
            {
                String file = item.Group.Header + "\\" + item.SubItems[0].Text;
                if (fullfilename.CompareTo(file) == 0)
                {
                    item.Checked = false;
                    this.listView1.Items.Remove(item);
                }
            }
        }
        private void starter(object sender, EventArgs e)
        {
            HashSet<string> filenames = new HashSet<string>();
            StringBuilder data = null;

            setguiLock(true);
            this.time2.Text = "";
            this.time1.Text = String.Format("{0:d/M/yyyy HH:mm:ss}", DateTime.Now);

            foreach (ListViewItem item in this.listView1.Items) {
                if (item.Checked) {
                    String file = item.Group.Header + "\\" + item.SubItems[0].Text;
                    if (File.Exists(file))
                        filenames.Add(file);
                }
            }

            string outputfile = output.Text;
            HashSet<string> words = null;
            if (File.Exists(output.Text))
                words = getHashset(outputfile);
            else
                words = new HashSet<string>();

            int filenamesnr = filenames.Count;
            int filenamesi = 0;
            foreach (String str in filenames){
                progresslabel.Text = string.Format("Progress: \t[ {0} / {1} ]", filenamesi++, filenamesnr);
                Application.DoEvents();
                data = new StringBuilder(System.IO.File.ReadAllText(str, Encoding.UTF7).ToLower());

                data = data.Replace("&auml;开发者_StackOverflow中文版", "ä");
                data = data.Replace("&ouml;", "ö");
                data = data.Replace("&uuml;", "ü");
                data = data.Replace("&otilde;", "õ");

                String sdata = new Regex(@"<(.|\n)*?>|%[a-zA-Z0-9]+?;|&[#a-zA-Z0-9]+?;").Replace(data.ToString(), "");

                foreach (string word in new Regex("[^A-Za-zšžõäöüŠŽÕÄÖÜ]+").Split(sdata))
                    if(word.Length>1)
                            words.Add(word);

                removefilefromlistview(str);
            }
            progresslabel.Text = "Progress:";
            putHashset(words, outputfile);

            foreach (ListViewItem item in this.listView1.Items)
                if (item.Checked)
                {
                    item.Checked = false;
                    listView1.Items.Remove(item);
                }

            this.time2.Text = String.Format("{0:d/M/yyyy HH:mm:ss}", DateTime.Now);
            setguiLock(false);
        }

        private void setguiLock(bool value){
            if(value){
                this.Enabled = false;
                this.button1.Enabled = false;
                this.listView1.Enabled = false;
                this.output.Enabled = false;
                this.openoutput.Enabled = false;
                this.progresslabel.Visible = true;
                this.Enabled = true;
            }else{
                this.Enabled = false;
                this.openoutput.Enabled = true;
                this.output.Enabled = true;
                this.listView1.Enabled = true;
                this.button1.Enabled = true;
                this.progresslabel.Visible = false;
                this.Enabled = true;
            }
        }

        private void button2_Click(object sender, EventArgs e)
        {
            if (!File.Exists(output.Text))
                   File.WriteAllText(output.Text, " ");
            System.Diagnostics.Process.Start(output.Text);
        }
    }
}

You need to get the right tool for the job. The quantity of data and markup in a linguistic corpus like this means you need a proper XML-aware indexing solution. Examples include eXist, XAIRA, CQP...