Talking to your gf's mom:
- Greeting: You say:
"Cháu chào bác ạ!" (It doesn't matter whether it's in the morning or in the afternoon)
She says:
"Chào cháu"- "How are you today?" --> You say:
"Dạo này bác khỏe không ạ?"- I'm fine, thanks, and you?:
+ If it's your gf's mom that say this ==>
"Tôi khỏe, cảm ơn cháu, thế còn cháu?"+ If it's you that say this ==>
"Dạ, cháu khỏe ạ, thế còn bác?"That's just some common greetings when Vietnamese people meet each other. Then depending on the time you may ask whether they've had meal or not (doesn't matter wheter it's breakfast, lunch or dinner):
"Bác xơi cơm chưa ạ?". Or you may ask whether she has to work today:
"Hôm nay bác phải đi làm không ạ?"Remember that it's just a formal question in Vietnamese. Westerners may not ask about things like this, but it's common to Vietnamese.
That's what Vietnamese people ask when they meet each other. The conversation would then continue depending on the relationship, situation...
If you have any question, feel free to ask, we are always willing to help people, especially when it comes to 'love' things