If you think it's hard in English, don't try to learn German then, grammatical cases are a pain in the butt.
A cat appeared on my back porch this morning. (New cat, no history at this point.) The cat then proceeded to shred the upholstery on every bit of furniture it could find. (We've already met the cat; using "a" in this sentence would introduce another cat.)
Of course John speaks a bit of Portuguese; he married a Portuguese woman. (We may have known John's wife for many years, but in this case she is merely one of a collection of Portuguese women. If we had used "the" in this sentence, it would imply that there is only one Portuguese woman in the world, or at least in the area, and that John married her.)
I am not a native English speaker so I may not be the best teacher of those details to a person speaking a different mother tongue than mine...
Latency was not a problem until it was below 100 ms then up to 500 ms it gradually decreased the quality of the conversation but not in significant way. Now at the 500ms mark something funny happened. The person thought that the other party had not heard what he said and begin repeating it while the beginning of the other person answer begin his phone. The comprehensiveness of the conversation decreased dramatically.
It was the same with noise - from a point on it was terrible. I think that accented speech could be considered as noise.
A friend of mine was doing project with Huawei a few years ago - the Chinese team was with strong accents and he was with very strong Eastern European too. They had trouble communicating in English.