- Change configuration settings for MySQL 
[client]
default-character-set = utf8mb4

[mysqld]
innodb_file_format = Barracuda
innodb_file_per_table = 1
innodb_large_prefix

character-set-server = utf8mb4
collation-server = utf8mb4_unicode_ci
skip-character-set-client-handshake

[mysql]
default-character-set = utf8mb4

– Adjust the $CFG->dboptions Array in your config.php to make sure that Moodle uses the right Collation when connecting to the MySQL Server:

$CFG->dboptions = array(
  …
  'dbcollation' => 'utf8mb4_unicode_ci',
  …
);

Source: MySQL full unicode support – MoodleDocs