He told me that for efficiency, they had different stages in the content rendering and that the main page structure didn't have your user information yet. That's rubbish IMHO because the accept language header should be readily available in that phase.
I've seen similar dysfunctions in other big orgs where a feature or bugfix would need to cross team boundaries and the outcome inhabits zones of vaguely defined responsibility.
The guy you argued with sounds like they were semi-justifying this with the typical "noogler" rose colored glasses.
He told me that for efficiency, they had different stages in the content rendering and that the main page structure didn't have your user information yet. That's rubbish IMHO because the accept language header should be readily available in that phase.