British and Irish people are quite used to hearing different accents within the UK and Ireland, in addition to encountering foreign accents. Consequently, they are often able to cope well with unfamiliar accents.
Teachers inevitably develop familiarity with the foreign accents of their students. This can mean that teacher can often understand their students far more easily that a typical English speaker.
English language learners may complain that they do not understand particular accents; this suggests that they could benefit from listening practice containing those accents.