You are welcome (to my house) is quite different from the very common but far from universal 'You are welcome' as a response to 'Thank you'. Duo Arabic needs to recognise this last one as an idiom, and accept some alternatives, eg 'Not at all', 'Don't mention it' or 'It's nothing'. I believe this is a big issue across many languages, ie an apologetic response to a thank you.
"Yaa" is a particle that is used when you address someone or call someone. In Old English it was "O/Oh": "O come all ye faithful", "O ye of little faith". We still sometimes use "oh" it to get someone's attention: "Oh, John!" In recent years, though, we seem to have replaced "oh" with "hey": "Hey, John!"