In US drama, i've seen people talk like this:
'Do you wanna have a dinner tonight with me?'
She talks like this way to her boy friend.
In another scene, a man also talks 'Do you wanna ~?' to his father.
I think 'Why do we~? ' is more common when you invite or ask someone to go somewhere with you.
But it may be different.
In what situation do you say 'Do you wanna~' ?
Also do you say to only friends? How about elder people or a stranger?
thanks.I almost forgot that wanna etc. were more casual.
I really appriciate your detail explanation.
I didn't know that there was like this difference.
"Why don't you have dinner with me?"
This sentence is a suggestion. It is used to suggest a solution to a problem. It is also used when you don't know if someone will agree, 'That sounds great!' or disagree, 'Thanks, but I can't'. Because it is used when you don't know if someone will agree or disagree, 'why don't you..' is also used with people you're not familiar with. INFORMAL & LOW-LEVEL FORMAL
Person 1: "I'm so tired! I can't believe I have to go home a cook."
Person 2: "Why don't you have dinner with me?"
The problem: Person 1 doesn't want to cook. Suggested solution: Have dinner with Person 2
Person 1: "I can't believe I'm running into you here! I haven't seen you in like what? Ten year!"
Person 2: "I know! It's been too long. Why don't you have dinner with me some time?"
The problem: Person 1 hasn't been spoken with Person 1 in 10 years. Suggested solution: Have dinner with Person 2. Note: It's been 10 years, Person 2 is not familiar with Person 1.
"Do you want to have dinner with me?" / "Do you wanna have dinner with me?"
This sentence is a general question. It is typically not used as a suggestion and it is normally used when you strong believe a person will say 'Yes'. Because you are expecting a 'Yes', it is mostly reserved for people familiar to you. INFORMAL.
Person 1: 'Do you wanna have dinner with me?'
Person 2: 'Yea sure.'
Person 1: "You need a break. Do you wanna have dinner with me then watch a movie."
Person 2: "I thought you'll never ask!"
If you would like to a more FORMAL way to ask someone to dinner, you'll say 'Would you like to have dinner with me'.
Wanna, gonna and gotta are slang abbreviations of their correct counterparts (want to, going to, got to).
I would say people usually use them when talking to friends and family, but not always.
Also, some people will use them all the time either because they are talking fast and/or they don't care about how they talk.
I hope that clarifies a few things.