In Irish it's "Fáilte ar ais"
"Gaelic" can mean "Irish Gaelic' or "Scottish Gaelic". They are classified as two distinct languages.
Fàilte gu Pàislig
Fàilte gu Wikipedia
Fàilte is the Scottish Gaelic for 'welcome'.
In Flemish, you say "welkom terug" to say welcome back.
You could say "welcome back" or "glad to see you home."
Tá fáilte roimh an Tiarna. (Irish)
You could say "Welcome back".
You can say "Dobrodošli nazad" in Bosnian to greet someone with "welcome back."
welcome back
welcome terug
You can say "Karibu Tena" in Swahili to mean Welcome Back.