PyCharm + Python + Flask + Jinja2 is enough to build web server/ajax and JavaScript + JQuery (maybe React). You can write small easy application but also extreme high scalable application.

I know Java but it need 4x time more code and code is not clear (too much forced use of @decorators) - too complex and takes more memory :)

Remember if you code in Python it is easy to code in Java but if you code in Java you must understand that Python is much more flexible and powerful - also easier to learn.