Please check the vhost.template for Nginx, lines 36-40:

# Environment.
# Possible values: "prod" and "dev" out-of-the-box, other values possible with proper configuration
# Make sure to comment the "ez_params.d/ez_prod_rewrite_params" include above in dev.
# Defaults to "prod" if omitted
#if[SYMFONY_ENV] fastcgi_param SYMFONY_ENV %SYMFONY_ENV%;

Uncomment the last line and set it to dev.

if[SYMFONY_ENV] fastcgi_param SYMFONY_ENV dev;

Test Nginx configuration.

nginx -t

You will see the following error:
2016/06/17 13:14:48 [emerg] 16933#0: unknown directive "if[SYMFONY_ENV]" in /etc/nginx/eZ/sites/ezpublish.enabled:33
nginx: configuration file /etc/nginx/nginx.conf test failed

I am using:

nginx version: nginx/1.4.6 (Ubuntu)

Just as a reminder, Nginx does not recommend the usage of IFs and I am not sure if it makes sense to use it in official vhost templates. Please check If Is Evil article on the oficial Nginx website.

Also, environment variables are not recommended. Please check:

• Environment Variables in Nginx Config
• Using Environment Variables In Nginx.conf