The description shown under the question mark is the Idea Campaign Description. This is added while creating or editing an Idea Campaign under:
Communities >> Modules >> Idea Board >> Campaigns
For multilingual communities, translations are generally managed from:
Communities >> Languages >> Manual Translations >>IdeaBoard Description. Screenshot for reference: https://prnt.sc/agAhjTHrFIL_
From there, you can select the required language and module, and add/update the translated text. Alternatively, either add the description in multiple languages within the same description field or create language-specific campaign text where applicable as a workaround.