Yes, I did something similar: prior to disabling Siri, I set Siri's language to French and kept the system language set to English (UK), but the Siri AI.app ("Siri" process in Activity Monitor) just keeps running despite Siri being indicated as disabled in Settings.
If you are on macOS 27, could you please open Activity Monitor, search (filter) for "siri" and see if a process called "Siri" is still running?
If you are on macOS 27, could you please open Activity Monitor, search (filter) for "siri" and see if a process called "Siri" is still running?