Server-side, I prefer PHP. Client-side there’s no choice - JavaScript. Desktop apps, I prefer Pascal (if no window is involved), VB or whatever other language is best for the use (even compiled PHP on some occasions). For Android, Java. For PIC CPUs, assembly.
For a new website, you’re going to have to use a server-side language, JavaScript, probably SQL, you should make use of AJAX (and you’ll need both HTML and CSS, even though they’re not programming languages) and, depending on the site, you may need other languages.