bug#57693: 29.0.50; Is there a more reliable version of `char-displayable-p'?

[Ihor Radchenko]

Eli Zaretskii <eliz@gnu.org> writes:

> So an efficient method of testing this for terminal would be:
>
>   . if terminal-coding-system is UTF-8, call internal-char-font to see

On my side, (terminal-coding-system) returns 'utf-8-unix
However, I imagine that other utf-8 variants may be returned, say, on
Windows.

Is there some standard way to know is a coding system is utf-8 or not?

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Ihor Radchenko,
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