You are architecting a Slack app to support a critical business process for a client's...

users.info provides the information required for both localization dimensions. Slack's user object contains timezone properties including tz, tz_label, and tz_offset. These values allow an application to schedule or render time-sensitive functionality according to the user's configured timezone rather than assuming the server's timezone or attempting to derive timezone information from HTTP headers. For language localization, users.info supports the include_locale=true parameter. When requested, Slack can include the user's locale, represented by an IETF language code. The app can then select translated strings and culturally appropriate presentation based on that locale. users.profile.get is intended for retrieving profile information and custom profile fields; it is not the preferred mechanism described by Slack for this combined localization requirement. HTTP request headers are also inappropriate for determining the Slack user's configured timezone because they represent network/request metadata rather than the user's Slack preference. Accordingly, D combines the appropriate API method with the two relevant user attributes. In implementation, the developer must remember to request locale explicitly using include_locale=true. This aligns with Design a Great User Experience, especially internationalization, localization, time-zone awareness, and tailoring application behavior to the individual Slack user.