Today I am going to write a quick post on how one can switch the language in bbPress forums as I saw someone asking about it on bbPress.org official forums.
Installing bbPress in a different language or changing it to a different language in an already installed bbPress follows exactly the same procedure. There is no difference in them as no permanent changes are made. In other words, nothing is written to the database. Obviously that doesn’t count the content you already have in posts.
Before you can switch the language, you would need the .mo file for your desired language. You can obtain the .mo file either from the Official server by Automattic - http://svn.automattic.com/bbpress-i18n/ or a local mirror maintained by ck @ bbshowcase.org - http://bbshowcase.org/forums/topic/bbpress-translation-internationalization-into-local-languages#post-1133
Now when you have obtained the language file, create a folder named my-languages in bbPress root for version 1.0+ and a folder named languages under bb-includes folder incase you are using version 0.9
Now open bb-config.php file (found in bbPress root), and edit this line.
define( 'BB_LANG', '' );
Change it to
define( 'BB_LANG', 'es_ES' ); // for Spanish language and a corresponding es_ES.mo file needs to be present in the language folder
That’s it. If you did both the steps correctly, then you should be able to check out the new language on your forums.
If you have any questions, then let me know and I will try to cover it up in a post.