I'm in the exact same situation, well, except for that time when for some unfathomable reason Google insisted, for weeks, to deliver what I believe is Lithuania

I'm in the exact same situation, well, except for that time when for some unfathomable reason Google insisted, for weeks, to deliver what I believe is Lithuanian to my home browser. Before the great Firefox extension purge I was sending out different language preference headers depending on domain. Unfortunately, this trick was already breaking down as more and more German companies redirect from their .de to their .com to show off ambition, leaving me with a bad English translation of the massive German due to headers. What I'd love to see would be a server side distinction between primary and secondary languages, but of course companies would lie their asses off for uncountable reasons bad and worse.