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

Simply change encoding of loaded file in IntelliJ IDEA IDE, on the right of status bar (bottom), where current charset is indicated. It prompts to Reload or Convert, use Convert. Make sure you backed up original file in advance.