@Chen.

This looks like a product / indexing issue rather than a configuration mistake, and there’s currently no confirmed solution posted on the Support Center yet. Pega Support Center First, confirm that mentions work if you search by Operator ID instead of full name; if that works, it reinforces that the problem is with how Japanese full names are handled in the search index. Next, re-index the operator and work indexes from Admin Studio and test again, as sometimes non-ASCII names don’t appear until after a clean reindex. Also check that your search node and Elasticsearch/analyzer settings support Japanese (UTF-8, proper language analyzers) and that pyFullName is included in the index. As a temporary workaround, you can keep an English “display name” or alias for operators so the mention list behaves correctly, while keeping the Japanese name in another field shown in the UI. If the issue persists on a clean Infinity ’23 environment with out-of-the-box Theme-Cosmos, capture tracer and browser network logs when you type @ + Japanese characters and raise a Pega Support ticket, as this is likely a defect that needs a hotfix.