[tubbzor]

you are going to see different langs here than what's generally trending at stackoverflow purely due to the culture that surrounds hn (which is start-up based), so you're going to see more Ruby, Python, Go, ect (although you should be able to search all those tags on SO as well).

In the industry (as far as what I read anyway), it seems mobile programming and 'Big Data' are currently at the forefront.

Web vs standalone: depends on the application. If there is a need to make it web-based...then make it web-based. If there's no need then why put in the extra work/resources.

It really is a very broad question, but you want to pick the best tools for the job. You wouldn't use a spoon to saw a tree down, similarly you wouldn't use Java for a car control system. The only way to know the differences is to dive a little into each language and learn it's pros/cons.