i install linux rh 6.2 with french env var and from source apache 1.3.12 and php 4.0.0 
/etc/scripts/i18n contains:
LANG=fr
LINGUAS=fr_FR:fr
LANGUAGE=fr
LC_ALL=fr

i use this very simple script:
<? 
 $var=1.123; 
 print("var=$var");   
?> 
It is displayed: 
var=1
 if i used $var=1,123; instead of $var=1.123; i have this parse error:
Parse error: parse error in /home/usr/local/apache/htdocs/double.php3 on line 2


If /etc/sysconfig/i18n contains:
LANG=en
LINGUAS=en_EN:en
LANGUAGE=en
LC_ALL=en_EN

It is displayed: 
var=1.123
of course...
with fr all the calculation are false