I update Japanese translation for Zabbix 1.8.5.

By the way, "S_CHART4_HEADER_TITLE_PART1" and "S_CHART5_HEADER_TITLE_PART1" are empty in en_gp.inc.php.

1414 // chart4.php
1415 'S_CHART4_HEADER_TITLE_PART1'=> '',
1416 'S_CHART4_HEADER_TITLE_PART2'=> '(year',
1417 'S_CHART4_HEADER_TITLE_PART3'=> ')',
1418 'S_CHART4_HEADER_DATE_FORMAT'=> 'Y',
1419 'S_CHART4_TIMELINE_DATE_FORMAT'=> 'd.M',
1420
1421 // chart5.php
1422 'S_CHART5_HEADER_TITLE_PART1'=> '',
1423 'S_CHART5_HEADER_TITLE_PART2'=> '(year',
1424 'S_CHART5_HEADER_TITLE_PART3'=> ')',
1425 'S_CHART5_HEADER_DATE_FORMAT'=> 'Y',
1426 'S_CHART5_TIMELINE_DATE_FORMAT'=> 'd.M',