BuddyPress.org

Hmm bp_create_excerpt fakes an excerpt on any content, whereas the_excerpt pulls the excerpt from a blog post. I don’t think you can except to change any/all of the calls and expect them to work.

I suggest you visit https://trac.buddypress.org/newticket and submit this as a bug report. I think it would be a good idea if you attach perhaps a text file or similar to the post with an example of non-English content that triggers this error on your system, so when Andy fixes it, he has a test case.