Which web language is required for onsite optimization ?
You should have basic knowledge of HTML, familiar with the structure of web application as well as CMS.
You need to know HTML, CSS as well as CMS knowledge for on page SEO Work When you going to do on page in your website then you need above language for keeping website's title, description, header, Alt-image, sitemap, Google analytic as well as webmaster tool etc.
For on page optimization, you don't need to know any kind of language. You just need to know HTML for maintaining your websites "title tag","meta description", "internal links" and many more.
You just need to know about site title Description, content, Internal Links, Speed and trust, and most important URL structure within all these you easy increase your site.