I need gurus in the house to tell me which programming was used to develop Facebook?

Php /mysql and some engines in c++ (initially), don't know of now.

Erlang was also used, but I should also believe they used javascript.

Facebook was written in PHP and JavaScript.

The LAMP stack.
Linus, Apache, Mysql and PHP.
C++ is also used at Facebook as it is confirmed that when Zuck was a teenager, he bought C++ for dummies.
The above I mentioned were the ones used at the earlier stage of Facebook.

there is no specific language cause I once read an article where mark zuckerburg said they allow developers to use programming languages of their choice to build Facebook, so some part might be c++, php, perl, python... but they mostly use php to display pages tho but other programming languages processes data at the lower end..

Facebook was strongly develop with php and then has their owned compiler which is hiphop was written with c/c++.

so for those of you who want to build a similar application like it. you need minimum of 4 expertise to help build ur dream.

you can talk to me on whatsapp +2347067212537. please no phone calls.

Large applications like Facebook often consist of many moving parts. Generally, such applications are not built on one stack alone. All the languages mentioned so far may be used for one component or the other.

However, two languages which I haven't seen mentioned so far are Java and Haskell. You may wonder, where are they used?

Java:
Presto, a distributed SQL query engine (https://prestodb.io)
Cassandra, a scalable column-family database (http://cassandra.apache.org)

Haskell:
Sigma, a SPAM bot (https://code.facebook.com/posts/745068642270222/fighting-spam-with-haskell/)
Haxl, a remote data access library (https://github.com/facebook/Haxl)

All these tools were built by Facebook and are still being used to power their back end. These are just the ones I know of.