What is the best language for a large resource engine?

Question

CMS

I am writing as a future customer who will need to find a permanent artist/-lei to write an engine for a resource with an expected top daily traffic of 500,000 unique visitors.
Content by categories and headings - hundreds of thousands of videos (from 360p to 2/4K), images (from 100x100px to 10000px) and audio; material output system (for a day, a week, a month, all the time with sorting according to different templates); a system of accounts (by groups) with registration by e-mail or through the social network API; comment system; the ability to upload your own content, forming a personal portfolio; question-answer system; system of subscription to the author/material and RSS; system of complaints and feedback; voting system; simple and advanced search system; internal analytics system, etc.
In short, the engine will be constantly updated and improved to meet the needs of a separate resource. However, there is a question of choosing a framework (sarcasm about your own is not appropriate). I focus on a high level of security and speed of the framework (subject to properly growing hands of the developer/s of the engine itself) with great potential for further expansion. I also want the framework to be requested from many developers, and not used by a dozen or two coders.
PS The cost of such a development in the ratio "from $..." also write, if you wish.

Answer 1

What you described is implemented on anything. Video processing will still be done on a separate server via *MQ which one, that is, little depends on the language that will be added to the processing queue. The rest is standard functionality.
Regarding performance: facebook/vkontakte is written in php, which, as it were, hints at the fact that the language itself does not play a role. twitter at first was on ruby, now ruby+scala. github - ruby.
If you take PHP, then take Symfony2 as a basis or take its components. This framework has perhaps the most developed ecosystem, many others are based on its components (including the popular Drupal). Well, in fact, in addition to zend2, for something serious and for growth, there is nothing to offer at all.
There is also Ruby with its rails and many other interesting frameworks.
There's also Scala, Python... there's a lot.
I can't advise on other languages. I recommend that you ask candidates not to explicitly indicate the stack of technologies, let them choose and argue for themselves.

Answer 2

The language is not important. The same php can handle with a bang. Framework.... well, since the orientation is for speed, then phalcon) If there is no desire to mess with pecl frameworks, then yii/laravel.