Getting the Language Files
Go to translate.wordpress.org/projects/wp-plugins/buddypress and select your preferred language.
At the bottom of the page, select all current as ‘.po’ and click on export. Save this file to a folder on your computer and do the same again this time selecting ‘.mo’
Please note that you can add your own translation by editing the POT file with Poedit.
Using the Language Files
Rename each file to
buddypress-language_COUNTRY.extension. For exemple:
Using FTP upload both the .po and .mo files to
/wp-content/languages/plugins of your WordPress instalation. If the folder does not exist, create it.
When all these steps are made correctly, BuddyPress should work perfectly in all the languages you added.