** This issue is addressed in ArcIMS 9.1 Service Pack 1 (SP1) **
The Client locale is not sent using TCP connections.
The class BaseEsrimapSimpleServiceProxy does send the client locale with the request using the HTTP send methods of the ConnectionProxy class.
But the AppServerLink class is not sending the client locale; this class is used by the ConnectionProxy class for TCP connection to an ArcIMS app server.
This was discovered by using an English-US locale metadata explorer web application, which uses the Java Connector, against a non-English US locale metadata server.
Metadata Explorer by default uses TCP connections. The App server log, with this setup shows that the locale from the client was not set, in which case, the locale that the app server uses is the app server's machine locale.