I found this guide over google but with broken links so i edited it a bit:
Create a data\local folder in your Diablo II directory. If your game is installed in "c:\Games\Diablo 2", you should have "c:\Games\Diablo 2\data\local"
You need to download a file called "diablofrtous.zip" and unzip it.
You also need a file: d2xtalk.mpq in english (Ask a friend that has the game in english to email it to you)
Then copy the "use" file into "c:\Games\Diablo 2\data\local".
Replace (after backing up the original) your d2xtalk.mpq by the one you have downloaded and renamed it.
Finally, add the command -direct to Diablo II shortcut (e.g. "C:\Games\Diablo 2\Diablo II.exe" -direct) and launch the game.
All the game will now be in English.
Or you can try this one out:
http://www.wikihow.com/Change-the-Game-Language-in-Diablo-II-Lord-of-DestructionOr you can use the client from blizzard though you will have to do a quick reinstall -