This would be fine.
UI is not needed, because i think we will set this once only.
Can you filter the top level like Baltic, Arabic,Turkey,...? would this be simpler?
Or if you prefer selection per cp, maybe this could be an solution:
IF NOT EXIST "<Encoding>"-section THEN
show all cp as default , like current state is
ELSE
use filter as set in "<Encoding>" and show this cp only
END IF
Because i think we will list up to 10 <Show cp="1252"/> only?
And this way around the <Show cp="1252"/> list will be shorter, then entering all possible CPs?
I think i need four CPs only, 1252. 850.UNICODE and UTF-16
BTW, as attachment i have provided an screen shot of code page installed on an MUL XP, for them not know how many there are

Thank you Alex , and please know no hurry is needed.