It appears that the first method can be refined further. Credit goes to Konoko from a certain Russian forum for figuring this out
Follow these steps:
1) Download the English language pack from here: http://rghost.net/59199883.
2) Extract DragonAgeInquisition.par into the "Dragon Age Inquisition" directory, overwriting the existing file (you may want to back it up first). Extract en.sb and en.toc into "Dragon Age Inquisition\Data\Win32\loctext". The default path for 64-bit systems is "C:\Program Files (x86)\Electronic Arts\Dragon Age Inquisition".
3) Make sure automatic log-in is enabled in Origin.
4) Close Origin. This is important! If Origin is already running when the game is launched, it will always force the game to start in the "Russian/Polish only" mode.
5) Launch the game directly by double-clicking DragonAgeInquisition.exe in the Dragon Age Inquisition directory, or use the desktop shortcut if you created one. The game will switch back and forth between the fullscreen and windowed mode a few times. This is normal. Origin will start AFTER the game is launched, and will have no effect on the locale. However, all online features will still be available.
6) Don't forget to close Origin after you exit the game. The "Automatically exit Origin after closing a game" option seems to be not working with the patched DragonAgeInquisition.par.
7) If you check for an update or do a game repair in Origin, you'll need to re-apply the patched DragonAgeInquisition.par file. The other two files (en.sb and en.toc) seem to be unaffected.
Please test this and see if it works for you. This might be a better option for those who feel uncomfortable using a third-party client.
P.S. DragonAgeInquisition.par from this pack is the original file patched by Outcome. So those who are already using Outcome may simply omit launching the Outcome client and start the game directly. Just make sure you don't have Origin running when you launch the game.