GLoc's l_date don't work.

Hi, are there anyone have used l_date to format a date object.

I have used it as:
<%= l_date porject.created_at %>

And defineded the "general_fmt_date" in "lang\en.yml" as:
general_fmt_date: %%m/%%d/%%Y

When run it, the output is: %m/%d/%Y

Maybe I had made some mistakes, who can hely me?