What is your welcome in Japanese?

In answer to someone's appreciation: 'O rei ni WA oyobimasen' => [lit: No thanks necessary]

'Dou itashimashite' => [lit: You're (very/most) welcome]

In welcoming someone's arrival:

'Irasshai mase' => [lit: Welcome!]

'Youkoso' => [lit: Welcome!] used less formally.

'Yoku kite kure mashita' => [lit: Good of you to come/Welcome!] Usually used with someone you know.