If you mean "join us together into one piece", then "Ceangail muid" would seem apprpriate. Literally "tie us". More emphatically "Ceangail le chéile muid" = "Bind us together" and is the name of a popular hymn.
If you mean "sit down here with us and have a drink", I would say "Bí linn" = "Be with us" ["Bígí linn" if you are asking a group to join you].
If you mean "join our organisation" then "Glac páirt/Bí linn/Bí mar pháirt ann"="Take part/Be with us/Be a part of it" [plural "Glacaigí páirt/Bígí linn/Bígí mar pháirt ann"] might do.
In Irish Gaelic it was usual to say Dia linn or "God with-us".
Is as Meiriceá mé (I am from America/USA.)
Mhothaigh muid uainn thú (literally) (felt - us - from us - you) It's a figure of speech in Irish, but it means "We Missed You"
Maith dúinn a Dhia, óir is peacaigh muid go Lá an tSléibhe
Irish Gaelic Séamus (shamus).
You have to be a US citizen to join the US marines i think its actually permanent resident
In Irish it's "Nár lagaí na bithiúnaigh do lámh"
with=le but if you are saying with me= liom , with you = leat, with he = leis , with her= leí with us=linn , with you(plural)=libh with them= leo. If you say an object or a name like with sarah it is just 'le sarah' .
"lin" should be "linn" "bígí linn" means "join us"
No, because "let's" means "let us", and it does not make sense to say "let us join us." It would be correct to say, "Come on, let's join them." It would also be correct, if you are speaking to someone outside your group, to say, "Come on, join us."
In Irish it's,ar ár son (for us)ar a son (for them)ar do shon (for you, singular)ar bhur son (for you, plural)
I think you will find it is Gaelic, which is encompassed in Welsh, Irish, and Scottish origins, I suppose it does go back to the Gauls who inhabited the French part of Europe, but for us in the UK it is Gaelic