You can say "Tud yma, boi!" (tid uh-ma boy) which is what I'd say, or if you wanna use the proper word for "boy" in Welsh then it's "bachgen" but it's less of a mouthful to say "boi", heh.
Formal: Dewch yma. Dere 'ma.
Hogyn or Bachgen
Dewch i mewn
Dewch ymlaen
you can't translate englsish phrases into welsh as you can words... so instead you could say , "byswn i'n dwlu taset ti yma" = i'd love it if you were here
Rydym yn cyfarfod yma.
ha'u ki' heni = come here ha'u ki' heni ta'ahine = come here girl ha'u ki' heni tamasi'i = come here boy foki mai = come back
"You are Welsh" = Rwyt ti'n Gymreig
Mae'n hyfryd cael bod yma.
To say "come here" in Hawaiian, you would say " hele mai."
'I am English' in Welsh is 'Dwi yn Saesneg'
To say come here girl in Spanish you would say, ven aqui, chica. You could say come here boy by saying ven aqui, chico.