When @ mentioning a user in Korean, listed results / search do not show while typing

Issue Summary

When @ mentioning a user with a korean name, and typing it with a korean keyboard layout, the automatic drop down search does not find users compared to typing english.

Steps to Reproduce

1. Setup a user with a korean name
2. Install a korean keyboard layout on your computer
3. Navigate to a pull request and start typing the korean name after an @ symbol (in a comment)

Expected Results

A dropdown list of users matching two characters or more begin to display.

Actual Results

No users appear in the dropdown.

Workaround

Add a space and then delete the space to trigger the user search.