For some places, there are more than one official languages, so if node title is created by phrases, it's can easily be translated to another language.
According to previous threads. Xenforo's doesn't allow node titles or description to be translated with its phrase system. On one of our site, we were forced to use both English and Mandarin on the title.
XenForo core does not handle multi-language content, so as you've pointed out it would end up with mixed content in one node without any programmatic possibility to tell that apart.
I'd (at least) create separate nodes per language.