BuddyPress.org

In your Plugin Directory create a folder and a .php file with this name: bp-strong-username-password

CODE:

<?php
/*
Plugin Name: BP strong username and password
Description: Force the new registered in BuddyPress to use strong username and password.
Version: 1.0
Author: Anonymous
*/

add_action( 'plugins_loaded', 'plugin_load_textdomain' );
function plugin_load_textdomain() {
  load_plugin_textdomain( 'bp-strong-username-password', false, dirname( plugin_basename( __FILE__ ) ) . '/languages' ); 
}

// Force Strong Username
function strong_username() {
 global $bp;

 if ( !empty( $_POST['signup_username'] ) )
   if ( !valid_username( $_POST['signup_username'] ) ){
    $bp->signup->errors['signup_username'] = __( 'Your username is not strong enough. Use uppercase, lowercase and numbers', 'bp-strong-username-password', 'buddypress' );
   }
 }
 add_action( 'bp_signup_validate', 'strong_username');

 function valid_username($candidate) {
   $r1='/[A-Z]/';  //Uppercase 
   $r2='/[a-z]/';  //lowercase
   $r3='/[0-9]/';  //numbers

   if(preg_match_all($r1,$candidate, $o)<1) return FALSE;
   if(preg_match_all($r2,$candidate, $o)<1) return FALSE;
   if(preg_match_all($r3,$candidate, $o)<1) return FALSE;
   if(strlen($candidate)<8) return FALSE;

   return TRUE;
}

// Force Strong Password
function strong_validation() {
 global $bp;

 if ( !empty( $_POST['signup_password'] ) )
   if ( !valid_pass( $_POST['signup_password'] ) ){
    $bp->signup->errors['signup_password'] = __( 'Your password is not strong enough. Use uppercase, lowercase, numbers and special characters', 'bp-strong-username-password', 'buddypress' );
   }
 }
 add_action( 'bp_signup_validate', 'strong_validation');

 function valid_pass($candidate) {
   $r1='/[A-Z]/';  //Uppercase
   $r2='/[a-z]/';  //lowercase
   $r3='/[!@#$%^&*()-_=+{};:,?<.>]/';  // whatever you mean by special char
   $r4='/[0-9]/';  //numbers

   if(preg_match_all($r1,$candidate, $o)<1) return FALSE;
   if(preg_match_all($r2,$candidate, $o)<1) return FALSE;
   if(preg_match_all($r3,$candidate, $o)<1) return FALSE;
   if(preg_match_all($r4,$candidate, $o)<1) return FALSE;
   if(strlen($candidate)<8) return FALSE;

   return TRUE;
}

—————-

For Translation: In your plugin dir, languages folder, create this file: bp-strong-username-password-es_ES.mo with this:

Þ•<\\K]\©H©O]ùuW]ÍForce the new registered in BuddyPress to use strong username and password.Your password is not strong enough. Use uppercase, lowercase, numbers and special charactersYour username is not strong enough. Use uppercase, lowercase and numbersProject-Id-Version: BP strong username and password
Report-Msgid-Bugs-To: 
POT-Creation-Date: 2017-07-15 19:42+0000
PO-Revision-Date: 2017-07-15 19:47+0000
Last-Translator: Anonymous 
Language-Team: Spanish
Language: es
Plural-Forms: nplurals=2; plural=n != 1
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
X-Generator: Loco - https://localise.biz/Forzar a los nuevos registrados en BuddyPress a usar nombre de usuario y contraseña fuertes.Su nombre contraseña no es lo suficientemente fuerte. Use mayúsculas, minúsculas, números y caracteres especialesSu nombre de usuario no es lo suficientemente fuerte. Use mayúsculas, minúsculas y números

And this file: bp-strong-username-password-es_ES.po with this:

msgid ""
msgstr ""
"Project-Id-Version: BP strong username and password\n"
"Report-Msgid-Bugs-To: \n"
"POT-Creation-Date: 2017-07-15 19:42+0000\n"
"PO-Revision-Date: 2017-07-15 19:47+0000\n"
"Last-Translator: Anonymous \n"
"Language-Team: Spanish\n"
"Language: es\n"
"Plural-Forms: nplurals=2; plural=n != 1\n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"
"X-Generator: Loco - https://localise.biz/"

#: bp-strong-username-password.php:17
msgid ""
"Your username is not strong enough. Use uppercase, lowercase and numbers"
msgstr ""
"Tu nombre de usuario no es lo suficientemente fuerte. Use mayúsculas, "
"minúsculas y números"

#: bp-strong-username-password.php:41
msgid ""
"Your password is not strong enough. Use uppercase, lowercase, numbers and "
"special characters"
msgstr ""
"Tu contraseña no es lo suficientemente fuerte. Use mayúsculas, "
"minúsculas, números y caracteres especiales"

#. Description of the plugin
msgid ""
"Force the new registered in BuddyPress to use strong username and password."
msgstr ""
"Forzar a los nuevos registrados en BuddyPress a usar nombre de usuario y "
"contraseña fuertes."