I'm a bit late to the party, but the only way Hubspot provides system page translations is to set up multiple domains. Then you can set the system pages for each domain.
I think a big big big minus in Hubspot is the lack of translation support.
While there is an option to translate a landingpage, there isn't an option to translate a blog post.. How weird is that? It really makes no sense.
System pages also don't have translations..
Text generated on the system pages comes from Hubspot, as far as I know you don't have control over them (you can edit the text, but to translate= nope..).
The only way I can think of is using specific text strings & then using javascript to replace texts..but that's not a real clean way imo.. Wouldn't want to start messing around with that..