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When the user is typing characters that cannot be encoded using the current encoding, the user should be notified of the fact and warned. For example, these characters could be specially highlighted (e.g. with red background) and the status bar could contain a brief explanation.
Now that issue #32392 ("Edit Text Rather than Escape Sequences") is fixed, everything is encoded using a pure ASCII characters and \uxxxx sequences - see also issue #75906 ("Add support for other encodings (other than ISO-8859-1)").