OP here. I only sent 3 emails from this very specific @fastmail.com email address in the past and it was way back in 2017. The email in question has never received email with the exception of this weird email in German language within a week of visiting Germany.
Could very well be apophenia. Germany was just one of the countries visited, and we all get spam in a variety of languages all the time, including German.
I've never received a spam email in German in my entire life. This spam email actually looks to be a legitimate email as after translating it the contents were basically to verify the email address. I don't think I've ever received an email in another language in my entire life and certainly not while I've been at Fastmail (10+ years).
The only foreign language spam I got was from Pokemon Go after I played it while visiting France & Spain. I received French and Spanish emails from them for years.
