Thank you for a question.
There is a problem with your MySQL settings.
If you are using MyISAM database engine this can be a known bug with MySQL related to MyISAM, the UTF8 character set and indexes that you can check here.
If you are using INNODB engine, then try to enable "innodb_large_prefix"
Please launch this command from your mysql console.
mysql> set global innodb_large_prefix = ON;
If it doesn't help, feel free to contact us.