As I study various languages I notice that there is a tendency to teach a language at a slow rate with emphasis on pronunciation. However the native speaker is often much faster and clumsier in their manner of speaking. It is more than just the accent. It is fast and lazy speech due to familiarity.
I know many people who have Spanish as their native language. They often bring their Spanish words into their English speech. One friend often asks “¿Por qué?” instead of “Why?”. This is commonly called “Spanglish”. It seems every culture does this.
The speaker will often do the opposite as well. They will incorporate English in their native tongue. I have heard various Asian languages with spattering’s of English phrases. The same is true in European based languages. It makes me think that the speaker has found a concept that means something in English that just doesn’t translate into their foreign tongue.
Some things are said confusingly by habit. The speaker is mostly unaware that they are repeating a certain phrase like “You Know?” until it is pointed out to them. At which point they make a conscious effort to avoid it. However they lapse back into the habit again when they are no longer monitoring how they speak.
I once asked someone where I might find a Christmas tree. They had a heavy Vietnamese accent and said something like “Ham Da Poe” and more clearly how many blocks away it was. When I got there I was staring at the sign on the store and only then realized that “Home Depot” was the name he was trying to tell me.
Why do some people get louder instead of slower? It is very confusing. Saying the same thing louder helps if one cannot hear too well. But annunciating and speaking each word clearly and more slowly is helpful for those of us still trying to learn your language. So instead of louder, speak slower please!