What is the best programming language to use for SEO?

Answer 1

SEO is search engine optimization.
Goal of SEI is to optimize web page to be first at google search or any other search engine.

Mostly it is using correct html tags, researching keywords and optimizing page for this keywords. Adding alt to images...
This is called "on page optimization".

And do backlinking - making sure other webpages are talking about your page and have link to it, this is hardest and most important part of SEO.

Answer 2

SEO is generally done in the HTML, CSS and JavaScript, front-end.