This is the latest discussion I heard about the issue:
https://bbpress.org/forums/topic/diacritic-letters-i-username-like-goran
What is the primary language of your forum?
Thanks for your replies. After reading / testing your links, I found a quick working fix. Here’s the plugin code :
<?php
/*
Plugin Name: UTF-8 usernames
Plugin URI:
Description: This plugin enable utf-8 characters in usernames. Mbstring must be enabled in the php.ini.
Author: Amir Habibi
Author URI: http://www.residence-mixte.com/
Version: 0.1
*/
function sanitize_user_mbstring( $raw_username, $username, $strict = false ) {
$raw_username = $username;
$username = strip_tags($username);
// Kill octets
$username = preg_replace('|%([a-fA-F0-9][a-fA-F0-9])|', '', $username);
$username = preg_replace('/&.+?;/', '', $username); // Kill entities
// Usage of 'mb_ereg_replace' instead of 'preg_replace' to preserve accents.
if ( $strict )
$username = mb_ereg_replace('|[^a-z0-9 _.-@]|i', '', $username);
return apply_filters('sanitize_user_mbstring', $username, $raw_username, $strict);
}
add_action('sanitize_user', 'sanitize_user_mbstring', 0, 3);
?>
To work, you must have mstring enabled in your php.ini.
Hope this will help !
chrishajer : our board is in french
great it works! but for choose a name to display on public (option in profil), a name with accents doesn’t work …
meitershaker : are you talking about the 1.0 alpha ?
amir: yes :p
ps: et plus précisément de la 1.0 trunk :p
meitershaker: 
be patient!!
my problem is already here 
little help please :p
It should be noted that using non ascii characters in bbPress is not supported and you could open yourself to a whole range of potential SQL injection threats by doing so.
WordPress has never supported non-ascii characters in usernames and has compensated by allowing display names, bbPress 1.0 now allows display names as well for the same reason.
sambauers,
may I ask why non-ascii chars for user name can make the threats of SQL injection etc greater?
@myu
It has to do with people using different character encoding for their database tables other than UTF-8. I’m probably overstating the threat as the same problem exists on all data input and we filter it out the problem there. I was also just reviewing WordPress injection attacks of days gone by, so it was on my mind.
In any case, the solution in the future is to change your display name after registration. Display names are UTF-8 friendly.
Thanks for reply.
Me, I personally don’t mind using alphabet for username, but have to think of target audience. Got me worried a bit. 
I hope in the future version there’s some sort of conversion mechanism for people that’s already registered using utf-8 encoded username. (pretty please..)
@ sam
“In any case, the solution in the future is to change your display name after registration. Display names are UTF-8 friendly. “
doesn’t work!!
me, 2 weeks ago:
“but for choose a name to display on public (option in profil), a name with accents doesn’t work … “
@ meitershaker
There was a bug in the display name implementation. First, update to the very latest trunk. There is a chance that you might have a user meta item for some users called ‘display_name’. This will be stomping on the real setting in the user table. Use this SQL query to clear out the bad data.
DELETE FROM bb_usermeta WHERE meta_key = 'display_name';
Once you’ve updated to the latest trunk and done that, you should be able to use any UTF-8 character in display names.
Will it be possible to upgrade to 1.0 when there’re people registering with utf8 usernames?
(I’m still testing and editing with 0.9, and will need utf8 names)
Or will it be better to use 1.0 alpha?
