Multilanguage BuddyPress with Polylang
1. Activate and setup the Plugins
At first yo need to have installed and activated the BuddyPress (configuring components and pages) and Polylang (added the languages you need in your site) plugins from WordPress.org. After you have setup BuddyPress and Polylang, you now can switch on the Multilanguage BuddyPress with Polylang plugin.
2. Add the BuddyPress Directory Pages for every language
You need to add every directory page you refered in the BuddyPress settings for every language again and add the translations to main language page on the right side of your page in the "Languages" box. If you have referenced it, BuddyPress should detect the translated sites and show the correct content on the sites (like the activity stream page, groups page and so on).
3. Install Emails in all languages
This plugin automatically adds the Emails if you use the BuddyPress tool to reinstall emails. It trashes the old emails and adds emails for every language you need. Be aware that you have installed all BuddyPress language files. Otherwise you have the possibility to add the Emails in the needed languages manually.
If you have any other ideas, please let us know and create an issue for this.