Have a similar issue with html layout:
Even though, my logback.xml contains

    <encoder class="ch.qos.logback.core.encoder.LayoutWrappingEncoder">
      <charset>UTF-8</charset>
      ...
    </encoder>

The output HTML file doesn't have meta charset attribute, which causes my browser (Chrome) to render the log file as ISO-8859-5 by default.

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