Board Thread:Anime/@comment-5774380-20180427103154/@comment-1327106-20180508013323

Unfortunately I doubt you'll be able to talk to him. He doesn't go abroad much and I doubt he speaks English. Your best bet (and it's not a very good one), is to write a physical letter in Japanese and send it to the appropriate address for Bessatsu Shōnen Magazine c/o Hajime Isayama. Isayama used to have a Twitter account but doesn't maintain it anymore, probably because as the series got more popular he got busier.

Manga-ka usually get fan letters through their publishers rather than directly through fans. There is a system set up for this, and in Japan it's a normal process. Everything is collected and sent on to the manga-ka.

After that, whether you get any response, would be up to Isayama. But that's probably your best bet to send him a message, barring any industry connections.