This snippet in page_header.php:
$error_msg = array(
new CSpan($failed_attempt, 'bold'),
_(' failed login attempts logged. Last failed attempt was from '),
new CSpan($attempip, 'bold'),
_(' on '),
new CSpan(zbx_date2str(_('d.m.Y H:i'), $attempdate), 'bold'),
);
error(new CSpan($error_msg));

Should use an ngettext call so it can be properly translated into some languages, and also a rewrite to using string parameters so that the entire string would be one sentence would ease the translation a lot.