It all comes down to:

You didn't do that.

If I have a mod_perl2 handler which just sends text/plain utf8 content and send those two strings via $r->print then I see different results in the browser (strA doesn't render correctly). Note that $r->binmode seems to do nothing.

You've shown that $r->print's expects a string of bytes just like the builtin print. If you want to output characters, you need to encode them manually or by telling the object to do it for you (such as by using PerlIO layer :utf8 or :encoding on a file handle) first.

The only reason $strB works is that $r->print does the best it can with an invalid input. You should get "Wide character" warnings alerting you to that fact.

You said binmode doesn't work on $r, so that leaves you with the option of doing it manually.

Fix:

$r->print($strA);  # XXX
$r->print($strB);  # XXX
[download]

$r->print(Encode::encode_utf8($strA));
$r->print(Encode::encode_utf8($strB));
[download]

utf8::encode my $strA_utf8 = $strA;
utf8::encode my $strB_utf8 = $strB;
$r->print($strA);
$r->print($strB);
[download]

Update: Adjusted phrasing