mail text has been garbled from a contact form

I've done to downgrade from PHP5 to PHP4. And then it happened. The mail text has been garbled from the contact form. I can't read the mail I received. I googled something relative word about it. Although it took a long time, finally I got the information to resolve it.

What I have to do is type the following magic word.

the sorce is written in EUC-JP

mb_language("Japanese");
mb_internal_encoding("EUC-JP");

the sorce is written in SHIFT-JIS

mb_language("Japanese");
mb_internal_encoding("SJIS");

the sorce is written in UTF-8

mb_language("Japanese");
mb_internal_encoding("UTF-8");

After I typed it, I read the mail text.