Likely to be useful for JEP-207.
From code inspection, I suspect that the simplistic treatment of this overload would also produce mojibake under some conditions in Pipeline builds, especially after
JENKINS-31096 ~ JEP-206: if a non-durable process emits non-ASCII text in some non-UTF-8 encoding, it will just be copied as is to the log. The fix would be to make the process launcher perform output trancoding to the charset specified in the TaskListener, assuming the source encoding is the system default on the node running the process (there is no API to specify the encoding in a ProcStarter).
Not a high priority for Pipeline since most such process executions are things like Git checkouts which are unlikely to include non-ASCII text. Would matter more for freestyle if logs were switched to UTF-8, as in JENKINS-48923.