Best way to convert text files between character sets?

Question

What is the fastest, easiest tool or method to convert text files between character sets?

Specifically, I need to convert from UTF-8 to ISO-8859-15 and vice versa.

Answer 1

There is also a web tool to convert file encoding: https://webtool.cloud/change-file-encoding

It supports wide range of encodings, including some rare ones, like IBM code page 37.