What you say matches my experience. I grew up speaking "local" English, but now my day-to-day language is "international" English. I find it funny when people compliment me on my clear and simple English, because when I talk to my family it's anything but.

In my job I deal with tons of non-native speakers, and in some cases I'll end up "translating" between two speakers who can't understand each other, even though it's all nominally English. This is especially the case when they're from different parts of the world and accent and native language strongly influence their speech.

Pronunciation is only one problem: Personally I find some British and most French natives harder to understand.

But native speakers from any continent can make me feel lost if they start to use a lot of idioms and slang expressions. My boss is an American who has lived abroad for a long time. I have usually no problems to understand what he means. In one phase I noticed him using an increasing amount of idioms I could not understand. When mentioning it to him he said he had had many telcos with US partners recently and that had probably inspired him to revive all kind of colorful idioms.

Offshore English is a concept to make the language more understandable to non-native speakers. Avoid rare words and idioms. Avoid everything that wouldn't be taught in foreign schools or common in your field. You won't get a Nobel prize in literature using it, but international colleagues will thank you.