Test & Make utf8mb4_general_ci for MySQL 5.5.x and later for better internationalization
MySQL 5.5.x later now supports UTF8mb4 encoding. And you should use this "UTF8mb-general_ci" collation for your concrete5 site.
Recently, more multibyte characters became available. However, due to the lack of the space, some of new multibyte characters are 4 bytes instead of 3 bytes. utf8_general_ci collation only supports 3 bytes characters.
If someone mistakenly used 4 byte characters under utf8_genera_ci environment, there is a risk of your DB is being corrupted.
If you are planning to make multilingual website, you should consider using or converting your DB collation to "UTF8mb-general_ci" for 5.7 site if your MySQL server is later than 5.5.x.