The first time I went to US, I was pretty confident in my English but natives didn't understand me. I could repeat the same, grammatically correct sentence 3 times and they still wouldn't get it.
Then I realized that in English (especially American English) you have to accentuate the right syllabus or they won't understand you. Say you're going to "mounTAIN view" instead of "MOUNtain view" and they have no idea what place you're talking about.