this won't work as it is joined before send to getttext `_`. working solutions are
```
_("There are some domains you have not activated:\n") +
   _inactiv_domains.join(", ") + "\n" +
    _("Do you want to write this configuration?")
```

or better one:
```
# TRANSLATORS: %s stands for list of inactive domains
_("There are some domains you have not activated:\n" +
   "%s \n" +
   "Do you want to write this configuration?") % _inactiv_domains.join(", ")
```
this way it is interpolated *after* send to gettext translation `_`.