If you do not wish to change character encoding for the entire server, but only one site (or only one directory) then this is possible to do using .htaccess.
AddDefaultCharset UTF-8
If you only wish to do this to php files (and not all files)
AddDefaultCharset UTF-8 .php
If you wish to modify the mime-type as well as the encoding (on html files in this example)
AddType 'text/html; charset=UTF-8' html
Tags: AddDefaultCharset, AddType, apache, apache2, charset, encoding, mime-type, php5, utf-8
[...] Make sure the right encoding is used to present the file (meta charset) / .htaccess or similar [...]
[...] get a html page to display UTF-8 encoded text correctly (without setting a default charset) simply add the following to the head of the html page. <meta [...]
[...] Setting a default charset using .htaccess is a simple thing to do [...]