Basically, Apple is using the browser language settings to choose interface language, so if you want to see it in English then you have to set your browser language settings to English. Of course, that it's a crappy solution, as then you have many other sites detecting English too. In general is a bad approach for this and many other sites, where you cannot override language settings. As Apple seems to don't care about this, the only more or less acceptable solution is installing another browser, set that browser settings to English (or the language you prefer), then use that browser for the App Store Connect site. I use Chrome normally, with language settings in Spanish, but I have Firefox language set to English. When it's important to see the English interface, I use Firefox.