Deprecate --locale support

[vuil]

Localization in the cf-cli is turned on via cf config --locale (some locale), but due to lack of maintenance of the CLI-side translations, doing so does not have the desired effects. Often, commands will have none, or just a small part of its output translated, leading to an uneven experience.

Unless the process of maintaining the translation is resurrected, we may want to consider deprecating the localization functionality instead of misleading the user, and cleaning it out from the code.

Relevant Slack: https://cloudfoundry.slack.com/archives/C032824SM/p1768979476036379?thread_ts=1768378778.410389&cid=C032824SM

[vuil]

Of the two (deprecating the functionality) and removing the code, my preference would be to deprecate the use of --locale, and retain the infrastructure in the code for the time being, in case there is renewed demands or a revival of the translation efforts.

[anita-flegg]

The section has been removed from the docs.
https://docs.cloudfoundry.org/cf-cli/getting-started.html

[beyhan]

+1 for the suggested by @vuil in #3703 (comment)