For a multilanguage site, using html_entity_decode without encoding type is risky to your website as in some cases, the translated language show weird characters.
In version of php prior to 5.4.0, if encoding omitted, default encoding value is ISO-8859-1, and UTF-8 auto set only from PHP 5.4.0
html_entity_decode($string, ENT_COMPAT, 'UTF-8')
Constant Name	Description
ENT_COMPAT	Will convert double-quotes and leave single-quotes alone.
ENT_QUOTES	Will convert both double and single quotes.
ENT_NOQUOTES	Will leave both double and single quotes unconverted.
ENT_HTML401	 Handle code as HTML 4.01.
ENT_XML1	 Handle code as XML 1.
ENT_XHTML	 Handle code as XHTML.
ENT_HTML5	 Handle code as HTML 5.
What do you think?