The real problem is that you are trying to get a single function to accept two different styles of arguments. As you see, that can get you in trouble.

If you want to change the check, eval { %{$_[0]} } works best to detect a hash.

sub better {
   my %params = eval { %{$_[0]} } ||  @_;
}
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But in this case, the following should do fine:

sub better {
   my %params = @_ == 1 ? %{$_[0]} : @_;
}
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Of course, you could always give the sub what it wants:

bad_but_typical("$i18n");  # Force stringification
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Update: Added missing curlies.