you can say don't mention it or most appreciated
ni hao (Chinese)
welcome abourd or welcome onboard is both good because the both make sence
"Tervetuloa [PLACE]+[END]." Enter the name of the place to the [PLACE]. But the [END] is very difficult to foreigners. You have to say the right kind of syllable at the end. These are combined...
The most appropriate reply would be "Thank you."