Convert latin1_* to utf8_

update.sql

ALTER TABLE wp_posts CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_520_ci;
UPDATE wp_posts SET post_content = CONVERT(CAST(CONVERT(post_content USING latin1) AS BINARY) USING utf8);
UPDATE wp_posts SET post_title = CONVERT(CAST(CONVERT(post_title USING latin1) AS BINARY) USING utf8);
UPDATE wp_posts SET post_excerpt = CONVERT(CAST(CONVERT(post_excerpt USING latin1) AS BINARY) USING utf8);
UPDATE wp_posts SET post_status = CONVERT(CAST(CONVERT(post_status USING latin1) AS BINARY) USING utf8);
UPDATE wp_posts SET comment_status = CONVERT(CAST(CONVERT(comment_status USING latin1) AS BINARY) USING utf8);
UPDATE wp_posts SET ping_status = CONVERT(CAST(CONVERT(ping_status USING latin1) AS BINARY) USING utf8);
UPDATE wp_posts SET post_password = CONVERT(CAST(CONVERT(post_password USING latin1) AS BINARY) USING utf8);
UPDATE wp_posts SET post_name = CONVERT(CAST(CONVERT(post_name USING latin1) AS BINARY) USING utf8);
UPDATE wp_posts SET to_ping = CONVERT(CAST(CONVERT(to_ping USING latin1) AS BINARY) USING utf8);
UPDATE wp_posts SET pinged = CONVERT(CAST(CONVERT(pinged USING latin1) AS BINARY) USING utf8);
UPDATE wp_posts SET post_content_filtered = CONVERT(CAST(CONVERT(post_content_filtered USING latin1) AS BINARY) USING utf8);
UPDATE wp_posts SET guid = CONVERT(CAST(CONVERT(guid USING latin1) AS BINARY) USING utf8);
UPDATE wp_posts SET post_type = CONVERT(CAST(CONVERT(post_type USING latin1) AS BINARY) USING utf8);
UPDATE wp_posts SET post_mime_type = CONVERT(CAST(CONVERT(post_mime_type USING latin1) AS BINARY) USING utf8);

Optional - ALTER TABLE wp_posts ENGINE='InnoDB';