We are aware of some reports from users saying they downloaded a language pack but cannot use that language in the game.
Localization is determined by the SKU you own and the system language setting—more info on what regions (SKUs) support what languages here.
Unfortunately, there is a bug right now where some incorrect language packs can be displayed. Please refer to this guide, for now, to understand what localization options your SKU supports while we work on an update to remove the incorrect options from the list.