The biggest issue I have when designing adventures is the same one I have when designing characters as a player: naming them. I know what I want their skills, history and personality to be, because that all has a tangible effect, but a name can be anything. If it can be anything, how do I narrow down what it SHOULD be?
It gets even harder when designing adventures with multiple characters, all needing a name. I can't share names and have fifteen Jims, but I don't want to end up with the three human tavern owners Jim, Nunzio and Kxarbutlko. Different names that sound like they fit together... Very tricky, personally.
And I don't wanna just use foreign words, because I live in fear of the day when a Spaniard asks me why I named a villain "cabbage" or something. And it's surprisingly hard finding a relevant word that actually sounds like a decent name.
When I start work on a new setting and have a rough general idea of the cultures that will inhabit it, I pick countries that I think are somewhat culturally comparable and look up lists with common names from those countries. Then I make myself a big list of names that I think sound like decent names for characters in my setting and copy them all into one big list of NPC names sorted by culture. If I need an NPC name later, I can go to that list. If nothing on the list seems fitting, I at least have a good pool of references for the sounds and letters that are common for that culture and can make up names that sound similar to the actually existing ones.