Which feature enables the determination of the language of each indexed document within a search solution?

The feature that enables the determination of the language of each indexed document within a search solution is AI skills within a Skillset. This capability utilizes built-in or custom AI skills to process data and extract useful information before indexing it for search. Within this context, language identification is a key skill that can be applied to documents to automatically detect which language they are written in. By including language detection as an AI skill in a Skillset, you can enrich your search index with this valuable metadata, allowing users to filter or query documents based on language.

Other options don't directly relate to the task of language detection for documents. For instance, the Custom Vision service is primarily designed for image classification and object detection rather than text or language analysis. The Document Analysis API focuses on extracting structured information from documents, such as form fields or tables, but it does not specifically identify the language of the text. The Content Enrichment module allows for the enhancement of content before it is indexed, but it does not inherently include language detection capabilities like the AI skills within a Skillset do.