Languages are spoken by communities, and "hobos" would not have a common language of their own. They might use the language of the region they are travelling through.
To express "good afternoon" in various languages, you would need to specify which language you're interested in. For example, you could ask:
* "How do you say good afternoon in Spanish?"
* "How do you say good afternoon in French?"
* "How do you say good afternoon in German?"
Let me know which language you're interested in, and I'll be happy to help!