With a Perl script I generate numerous Google Line Charts for 20 and more series of data at once.
The legend labels are of the form: a serial number appended by an i
To get full legend in your chart just add chartArea width and height as below
var options = { title: csv, width: 800, height: 600, chartArea: { width: "50%", height: "70%" } };
Take a look at this jqfaq.com to get a working sample