Good morning. This is Infra Miyashita.
The graph settings of zabbix are not displayed in Japanese by default. *This is when the item name is in Japanese.
The operating environment looks like this.
OS: CentOS release 6.5 (Final) Version: zabbix-server-2.2.3
If you look at the graphs created with "Monitoring Data" → "Graphs", the Japanese parts will be □ as shown below. This is due to the fact that the item uses Japanese and there is no font when converting the image.

First, check where the font is placed.
# ls /usr/share/zabbix/fonts/
graphfont.ttf
Next, check the fonts installed in the OS.
$ ls /usr/share/fonts/
dejavu ipa-gothic ipa-mincho ipa-pgothic ipa-pmincho vlgothic
Use IPA. Just put up a symbolic link and it's OK. In particular, you don't need to restart zabbix-server.
# ln -s /usr/share/fonts/ipa-pgothic/ipagp.ttf /usr/share/zabbix/fonts/ipagp.ttf
# vi /usr/share/zabbix/include/defines.inc.php
(Changes)
7
39c39
< define('ZBX_GRAPH_FONT_NAME', 'ipagp'); // font file name
---
> define('ZBX_GRAPH_FONT_NAME', 'graphfont'); // font file name
86c86
< define('ZBX_FONT_NAME', 'ipagp');
---
> define('ZBX_FONT_NAME', 'graphfont');

In this way, the graph was also displayed properly in Japanese.