When users start a new translation, they may not have a clear idea on what to translate. Currently users can select the article and try to translate in order to get a warning otherwise. However, a more fluent approach may encourage users to search for more topics to translate.
This task requires design work to find the specific solution, but it may involve surfacing (e.g., in the the auto-complete menu) whether the articles are available/missing in the target language, and or reorganising the new translation dialog.
It may be worth exploring in the context of T96147: [Epic] ContentTranslation - Lists of articles to translate since article look up seems an essential part of it.