Wow, do I ever relate to this:

It takes me a while to compose my thoughts. Often, when I should speak, I don’t, or can’t, because I don’t have the right words at the right time, and my silence is considered rude or inappropriate.

Except, far too often, I do blurt something out. Always regrettable. If you can find a safe platitude or innocuous comment - YOU GO!! - and I need to remember the Mortification of Silence along with saying the "safe," neutral, helpful things, not the terrible "OMG, how awful, your dad is dead" type of outburst.

Cultural differences and expectations - yes!
Americans are known for being blunt, with not enough of a social filter.
Going back to those 1800s Henry James novels...

Thanks for the kind words and oh-so-relatable confessions.