addslashes() is the general solution to this - committed, thanks for 
the heads up. As for the HTML validation errors, does the backslash 
both solve the validation issue and not create other side effects?

In the Calendar Management screen,

the newChoice function is broken by JavaScript that does not compile.



the two lines like this:

urlObj.innerHTML = '<em><?php echo _("Select a calendar above to 
display the URL") ?></em>';

break when gettext returns a string containing a single quote, i.e. in 
the fr_FR translation



Also, </em> throws a warning as to html validation, because the "/" 
must be escaped ("<\/em>")



I do not know if this is an ideal solution, as it would now break with 
double quotes.