Slack locale information is explicitly opt-in at the API-request level. For a conversation, an application can call conversations.info and set include_locale=true. For an individual member, it can call users.info with the same parameter. Slack then includes the applicable locale field in the returned object. The locale is represented using an IETF language identifier such as en-US or another supported language-region combination. Slack's design guidance recommends using a conversation's locale for content published publicly within that conversation and using the individual user's locale for private or personalized interactions. Option C is incorrect because locale is not included automatically by default. The application must explicitly request it. Option A incorrectly treats locale retrieval as an app-dashboard configuration toggle rather than a Web API argument. Option D refers to API methods that do not exist; Slack uses established methods such as users.info and conversations.info. Applications should also retrieve current locale information when preparing content rather than permanently assuming a user's language preference, because those preferences may change. This directly aligns with Design a Great User Experience, particularly internationalization and localization of Slack application content.