Japanese encodings seem to not be working

When using the Decode Text operation, the 3 JIS encodings all return errors like this:

Unrecognized CP: 50220

I don't know enough about char encodings to provide any extra details.

Start with the Decode Text operation and reproduce the failure for each of the three JIS encodings. Trace how those encodings are handled when the operation reports "Unrecognized CP: 50220"; done means all three no longer return that error and have suitable coverage if the project provides tests for the operation.

Written by the indexing model from the issue text.