Formal:
* Dobrodošli natrag: This is the most formal way to say "welcome back" and is appropriate for official settings or when addressing someone you don't know well.
* Dobro došli opet: This is another formal option, slightly less formal than "Dobrodošli natrag".
Informal:
* Dobro došao/došla: This is the most common and informal way to say "welcome back" and is used among friends and family. You'll use "došao" for a male, "došla" for a female, and "došli" for a group.
* Vratili ste se/ste se vratili: This is a more literal translation of "you have returned" and can be used in both formal and informal contexts.
You can also use a simple "Dobar dan" (Good day) or "Zdravo" (Hello) if you're just greeting someone who has returned.
Remember that Bosnian uses different forms depending on gender and number. So, be sure to choose the correct form based on who you are addressing.