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

If macOS GUI applications are your bread and butter, SubEthaEdit is the text editor I usually go to for encoding-wrangling — its "conversion preview" allows you to see all invalid characters in the output encoding, and fix/remove them.

And it's open-source now, so yay for them