Change Log4J2 appender encoding dynamically - log4j2

Question

Log4J2 2.17.2 (or newer)
I have a "console" application generating a report from a product. The product data are in UTF-8 format.
When I run the application in windows cmd shell (CMD), the following (simplified) appender is working fine,
and all the encoding looks fine. So also german Umlaute are converted properly without any additinally programming.
<Console name="STDOUT" target="SYSTEM_OUT">
<PatternLayout pattern="%m%n" charset="CP850" />
So CMD is using the CP850 encoding.
I also can run my application from within a product, so I get as runtime environment an UTF-8 encoded outputstream.
Testing with
<Console name="STDOUT" target="SYSTEM_OUT">
<PatternLayout pattern="%m%n" charset="UTF-8" />
is working fine from this environment.
My log4j2 configuration is part of the application, read via class path. More or less similar to log4j2.xml
So I'm looking for a dynamic way to switch. I can launch my program e.g with a swith/flag if necessary.
Any hints?
Uwe
EDIT after Piotr's answer:
The answer from Piotr (Thanks) brought me to the following solution,
using the variable substitution and the ThreadContext.
main
boolean cmdMode = ...
String charSet = cmdMode ? "CP850" : "UTF-8";
ThreadContext.put("CHARSET", charSet);
In the log4j xml, I used:
<Console name="STDOUT" target="SYSTEM_OUT">
<PatternLayout pattern="%m%n" charset="${ctx:CHARSET}"/>
Works fine.

Answer 1

The console appender can create a pattern layout with the correct encoding if none is provided. So if %m%n is enough for you, just omit the layout configuration:
<Console name="STDOUT" target="SYSTEM_OUT"/>
If you need a different pattern we incur in a limitation of the plugin builder (cf. LOG4J2-3372): the layout is created before the console appender, so the appender can not modify the encoding used by the layout. You can however apply the same logic used by Log4j2 in your configuration:
<Properties>
<Property name="sun.stdout.encoding" value="${sys:file.encoding:-UTF-8}"/>
</Properties>
<Appenders>
<Console name="STDOUT" target="SYSTEM_OUT">
<PatternLayout pattern="%d [%t] %p - %m%n" encoding="${sys:sun.stdout.encoding"}"/>
</Console>
</Appenders>
This should work because:
Java applications that run from the console, have the system property sun.stdout.encoding correctly set,
applications that don't run in the console will have file.encoding set to the default system encoding.
in the unlikely event that file.encoding is not set, UTF-8 will be used.