If your MySQL server does not support the collation: ‘utf8_unicode_520_ci’, this can easily be fixed by :
you can simply open the .sql file in a text editor such as Notepad++, and use the ‘find and replace’ tool:
replace: utf8_unicode_ci with utf8_unicode_520_ci
Once all instances of utf8_unicode_520_ci have been replaced with utf8_unicode_ci, you should then be able to import the database as normal.
if you are facing this error Collation ‘utf8_unicode_ci’ is not valid for character set ‘utf8mb4’database import
try this solution