is there anyway that i can do that? i downloaded gog version but there was't any language choosing option, what can i do?

Looking for this amswer too

Have you downloaded the game from the website or using Galaxy?

If you use Galaxy, try changing the language in the Fallout 3: Game of the Year Edition gamecard in your library. But if you don't use Galaxy...

I found a very old post elsewhere on the Internet that claims you can change gameplay language by editing an .INI file. Go to C:\Users\your Windows username\Documents\My Games\Fallout3 and open FALLOUT.INI, search for a variable called sLANGUAGE, and try changing the language after the "=" to SPANISH, ESPANOL, or ESPAÑOL (I have no idea which one the game will recognize -- the post was about changing to English, rather than away from it; in any case, the variable name must be in all caps).
This advice, however, is from about 2011, so even if it worked back then, the way the game's localizations are packaged could have changed since then.

If the .INI edit doesn't work, you'll probably be stuck re-downloading and re-installing. There are slight differences in the size of the backup installer depending on which language you select in the library entry; coupled with the utter lack of any normal way to change language, this likely indicates that the different language versions of the game are entirely separate. This means you'll have to re-download the entire multi-part installer (Spanish-language version this time) and re-install. I would imagine that any saves and settings will carry over regardless of language, so at least there's that.

Yes, languages are entirely separate.

http://www.gogdb.org/manifest/c5d11677a290d438440fafc9138988b2
( http://www.gogdb.org/product/1248282609 )
As always for steam\gog\etc +retail, it is not 100% correct list for languages depots. And this if for GOG Galaxy version - such versions are differ from offline builds time to time and sometimes even miss content (offline is superior version, rarely).

Here you can find main txt and sound files are differ from list above (fra vs eng)
http://www.gogdb.org/manifest/680c557ce2f069a6c1769c7f480258fd
but there is some equal (and most likely really same files) txt\sound for additional and\or for DLCs content files.
(Video folder is entirely differ)

This game do not support change-language option. Although it probably used option language=ENG\.etc in ini file, it stil lrequire replace at least few files in Data folder and they are not separated from each others.

So to change language you should use GOG Galaxy (even if initially installed as offline - should be a way to 'install' to galaxy), or compeltely reinstall from separate localised installer.

Do not forget for GOG Galaxy te do verify game files - at least twice in a row. Galaxy now always redownlaod something - it is normal for him.