UTF-8 does not require BOM, but for UTF-16 and UTF-32 BOM is always 
present. Files with UTF-16 and UTF-32 without the BOM should be 
identified as binary.

But why there are no plans to support UTF-16 and UTF-32? Diff is part of 
the Git and is used all over the world. Now 2018 and Unicode solved 
problems with encodings.


17.04.2018 10:37, Paul Eggert:
> Keepun wrote:
>> Files with encoding greater than 8 bits without BOM at the beginning 
>> can be immediately identified as binary.
>
> No, the BOM is not required or recommended in UTF-8, so it would be a 
> mistake to identify GNU/Linux text files as binary merely because they 
> lack a BOM. Typically these files do not have a BOM, and when they do 
> one of the first things many users do is remove the BOM because it can 
> cause trouble in practice.
>
> Diffutils does not support UTF-16, where a BOM would make more sense, 
> and there are no plans to add support for UTF-16 (or for UTF-32, for 
> that matter).