It's a West African slang mostly used by Nigerians. When said, it's used to show respect, appreciation or salute someone with higher reputation or swag than you, or even jokingly with friends and family, most especially when you want something from them. For example: help or mostly money. It's said before and after the request has been granted.
In other words it's used for praising a person in other to get something.
When I saw the chief coming, I raised my hands up, stomped my feet and shouted, "twale sir!" and he gave me 50 Bucks immediately!
Verb: Texting while walking really slowly in no specific direction much to the annoyance of anyone behind you who is walking at a normal pace that are either blocked, or need to walk around you. Noun: twalker
Sorry I'm late, I got stuck behind a twalker
I need to quit twalking and pay attention to where I am going
I had to crawl through this twalker's legs to get past him/her
Sorry, I've been twalking in circles