About nine years ago, as a young pup, I recall meeting a Programme Director from another organisation. Having just come back from years in a field office, she was gaunt from tropical diseases, and wrinkled and weathered from years of sun exposure. Her clothes looked like they were from another decade. She wore no jewellery and no make up. She spoke slowly and deliberately, using simple words and short sentences. No jargon. No sophistication. Plain speaking. Every few minutes, she would pause and check that you got her point. I recall another colleague saying derisively, "You can tell when they have been in the field too long. They lose touch".
Not that I have reached this point yet (and hopefully I never will), but I've already noticed a developing tendency to dumb-down my vocabulary and simplify my speech in order to communicate with the locals. Even those that speak English well are somewhat limited in the more complex vocabulary and sentence constructions. It's easy to forget that when the person you're talking to is nodding and saying "Yes, yes" over and over again he might not actually be understanding everything you're saying.