Page Title

1 . web development

A . front end

html
css
javascript

frameworks and libraries for front end

css
(bootstrap , materialize , sass , bulma , tailwind , semantic ui )
js
( jQuery , react.js , angular.js , ember.js , backbone.js )

B . database

sql
mysql
mongodb

c . back end

php
c++
c#
java
python
javascript
node.js
ruby

frameworks and libraries for back end

js
(express.js , next.js , meteor. js , nust. js ,..)
python
( django , flask , web2py , cherrypy , bottle , sanic , ..)
php
(laravel , codeIgniter , symfony , cakephp , yii , phalcon , ..)
java
(spring , hybernate , struts , GWT , JSF , ..)
Ruby
(ruby on rail , hinami , sinatra , cuba , ..)

2 . Android app development

java
(mostly use)
kotlin
(good for newbi in app dev.)
dart
(for android and ios app both in flutter )
c#
(html+css+js)

3 . IOS app development

objective-c
swift

4 . Hacking related

python :-
(for testing + automation + developing( network-tool , script )
sql :-
(for query and fetch info from database , sql injection,obtain unhash password)
Node.js :-
(for building internet worms , mimicking server and client side attack both )
Assembly :-
(for manupulating low level system ,malware like virus and trojon ,but a little hard to master )
PHP :-
(for accessing form and set data to vulnarabling server.)
Ruby :-
(for exploit development.)

5 . Game development

Lua
(ex - for agen,amulet)
java
(ex - for jake2 , java3d)
c++
(ex - for unreal,0gre)
c#
(ex - for unity,unigine)
javascript
( ex - for playcanvas , phaser )
html+css+js

6 . robotics

c & arduino
python & respberry pi

7 . artificial inteligence

python
lisp
java
c++
prolog

8 . Software development

Python
Java
c++
Scala
javascript

9 . data scientist

python
R
java
sql
julia
scala
matlab
tensorflow

10 . machine learning

python
(scikit , tensorflow , keras , theano )
c++
(mlpack , shogun , tensorflow)
c#
(Ml.net , tensorflow)
python , java , c++ , javascript , go , swift are supported in tensorflow ( open sorce machine-learning framework)

note :- I don't say , only these are languages for respective purposes but you can use one of these languages for corresponding purposes . I know i have left various languages , Comment below if you know other languages for any of these/new purposes . i will add them here .

which language to learn