BBC Article "Native English speakers are the world's worst communicators" (link
below)

When such misunderstandings happen, it’s usually the native speakers who are to
blame. Ironically, they are worse at delivering their message than people who speak
English as a second or third language, according to Chong.

But… often you have a boardroom full of people from different countries communicating in
English and all understanding each other and then suddenly the American or Brit walks
into the room and nobody can understand them.

The non-native speakers, it turns out, speak more purposefully and carefully, typical of
someone speaking a second or third language. Anglophones, on the other hand, often talk
too fast for others to follow, and use jokes, slang and references specific to their own
culture, says Chong.

The native English speaker… is the only one who might not feel the need to accommodate
or adapt to the others, she adds.

Dale Coulter, head of English at language course provider TLC International House in Baden, Switzerland, agrees: English speakers with no other language often have a lack of awareness of how to speak English internationally.

Those native English speakers who are EFL/ESL TEACHERS who can speak a second language,such as Welsh or German or French or Gaelic will usually have the awareness necessary to speak English internationally.