Unfortunately there currently isn't any support for this.. the language is automatically determined from the browser. There may be some browser tricks you can use to do this.. e.g. if you're allowed, set up a separate link on your desktop/quick launch bar to launch firefox with a different profile and with english set. Or perhaps reserve a different browser for this task.

Another option would be to actually remove the italian translation from RTC itself so that it always falls back to the default (english), e.g. reinstall RTC but in the install manager, don't check the Italian language option. But that seems a bit drastic.