I had English language in iTunes Connect, but today it's changed to russian (I'm from Russia) and I cant find where to change the interface's language back to English (Russian localized - bad).
Found that very frustrating too (I'm Russian as well). It based on your "preferred language" settings in browser. If you use Chrome, it can be found there chrome://settings/languages, move "English" upper. That's it.
Maybe something has changed over the time, but the previous approach didn't work for me. My solution (macOS Sierra):
- Open "System Preferences"
- Open "Language & Region". There is list of "Preferred language" on the left panel. Click on the button "+" under the list and add English language as primary.
- Reboot you mac.