include('config.php'); //My database data for connection

if(isset($_POST['submit'])) {
    $username = $_POST['username'];
    $password = $_POST['password'];
    $email = $_POST['email'];

    $query = "INSERT INTO account SET username = '".$username."', password = PASSWORD('".$password."'), email = '".$email."'";
    $execute_query = mysqli_query($connection, $query);
    if($execute_query) {
        //Creates the account
    }
    else {
        //If an error occures
    }
}

Username: Luís
Password: 1234
E-mail: [email protected]

Creating a DataBase and Table with:
utf8_general_ci
utf8_unicode_ci
utf8mb4_general_ci
utf8mb4_unicode_ci
latin1_swedish_ci

ALTER DATABASE [name of your database] CHARACTER SET utf8;

ALTER TABLE [name of your table] CONVERT TO CHARACTER SET utf8;

ALTER TABLE [name of your table] MODIFY [name of your column] [other settings] CHARACTER SET utf8 COLLATE utf8_general_ci;

CREATE DATABASE [name of your database] CHARACTER SET utf8 COLLATE utf8_general_ci;

[client]
default-character-set=utf8

[mysql]
default-character-set=utf8

[mysqld]
collation-server = utf8_unicode_ci
init-connect='SET NAMES utf8'
character-set-server = utf8

include('config.php'); //My Database data for connection.
//Connection set with $connection = mysqli_connect($mysql_host, $mysql_user, $mysql_pass, $mysql_db)

if(isset($_POST['submit'])) {
    $username = $_POST['username'];
    $password = $_POST['password'];
    $email = $_POST['email'];

    $connection->query("SET NAMES utf8"); //FIXED (Gets $connection from config.php and runs the query "SET NAMES utf8")
    $query = "INSERT INTO account SET username = '".$username."', password = PASSWORD('".$password."'), email = '".$email."'";
    $execute_query = mysqli_query($connection, $query);
    if($execute_query) {
        //Creates the account
    }
    else {
        //If an error occures
    }
}