Selenium officially supports Java, C#, Python, Ruby and Javascript
(Node).And also supports third party languages PHP, R, Object c
which were not developed by Seleniumhq.Usually languages can
be selected based on the development environment.The reason
behind is , even after the script development the developers can
write automation scripts.
There is no relation between choosing the languages for selenium
webdriver and the application development.We can choose any
language which is comfortable to write automation scripts.

There is a feature within Selenium IDE to convert its own scripts
to webdriver scripts.However, if you want any tool to convert the
scripts, Contact us.

SAP TAO, UFT, ECATT, TestComplete can be used. UFT has a good
support for automating SAPgui and SAP CRM as well.

The webservices play a vital role in the modern development, we use
SoapUI (open source - Groovy framework).JMeter, REST Assured, Java
libraries.

For web applications Selenium webdriver plays most and for desktop applications UFT stays dominant.

Select frameworks for Selenium webdriver based on the
languages as given below.
For Java: - Testng,junit,cucumber,jbehave
For C#: - Nunit,Specflow
For Python: - Unit test,Robot
For Ruby: - Cucumber,Capybara
For Javascript: - Jasmine,Mocha,NightwatchJs
For PHP: - PHPUnit,Behat
Page object model,Test data handling,Reporting,CI integration
should also be taken care along with Frameworks.

Of course,We can. Nowadays, Selenium scripted bots are widely
used for web scrapping,Chat auto-reply etc.

Mobile apps can be automated using Appium,Selendroid,Robotium
and Calabash.