I got a solution, which should be 100% legal as well, as you need to take some additional money into your hands.
Get the Download-Version from Gamestop which essentially is a Steam-Code.
Update your Steam-Client to the Beta-Version before or after activating the code.
Get rid of the gamefolder in your steamfolder (I advice just renaming and then "deleting" the local gamefiles in steam)
Reinstall using English language.
I am at exactly that step right now and a test-start of the game showed an all English setting. The attempt to convert all files using the TTW-Installer is running right now.
Edit:
Test done... Installer had run without any issues... I skipped the addon-files with a rebuild as I they had no issues, including sound, if I remember correctly, all other I made sure to rebuild them even if they already had been present from last attempts.
[b][u]My Steam Profile[/u][/b] [i](from [URL=http://steamdb.info/calculator/?player=76561197988497901&country=us]SteamDB[/URL])[/i]
[list][*][b]Worth:[/b] $3326.99 ($1368.22 with sales)
[*][b]Games owned:[/b] 216