Have you tried the code styling plugin ?
Please also share your server php error log to check this (upload it somehwere online and share its link here .)/
So it seems like it is an issue with the loco translate and the buddypress plugin itself .
Now to translate the buddypress strings I would recommend you to use either code styling plugin .(note that it will no affect any other plugin translation if you just edit and save the transaltion files of buddypress plugin only )
Or
Use the po editor .
for po editor follow this link : http://www.wpbeginner.com/wp-themes/find-translate-translation-ready-wordpress-theme/