Unable to tag usernames with accents in them

[neoncube2]

Current Behavior

A user of my forum has the username Xhéres . I'm unable to tag him in posts, likely because his username has an accent in it.

Steps to Reproduce

1. Register a user with the username Xhéres
2. Try to tag the user in a post. The username is autocomplete correctly:

3. After posting, the user is not correctly tagged. Xhéres shows up as not tagged, while all of the others users are successfully tagged:
   

Expected Behavior

Tagging users with accents in their username works.

Screenshots

No response

Environment

• Flarum version: 1.8.9
• Website URL: https://forum.mylittlewordland.com/d/4949-every-ttmik-lesson-levels-1-10
• Webserver: Apache
• Hosting environment: VPS
• PHP version: 8.2.13
• Browser: Firefox 136

Output of php flarum info

Flarum core: 1.8.9
PHP version: 8.2.13
MySQL version: 10.3.39-MariaDB
Loaded extensions: [hidden]
+------------------------------+---------+--------+
| Flarum Extensions            |         |        |
+------------------------------+---------+--------+
| ID                           | Version | Commit |
+------------------------------+---------+--------+
| flarum-tags                  | v1.8.3  |        |
| flarum-suspend               | v1.8.4  |        |
| flarum-mentions              | v1.8.5  |        |
| flarum-subscriptions         | v1.8.1  |        |
| flarum-markdown              | v1.8.1  |        |
| tpokorra-post-notification   | 0.4.8   |        |
| noriods-auto-more            | v1.0.0  |        |
| fof-user-bio                 | 1.4.2   |        |
| fof-upload                   | 1.7.0   |        |
| fof-split                    | 1.1.1   |        |
| fof-sitemap                  | 2.2.1   |        |
| fof-profile-image-crop       | 1.1.6   |        |
| fof-pretty-mail              | 1.1.2   |        |
| fof-polls                    | 2.2.9   |        |
| fof-nightmode                | 1.6.0   |        |
| fof-merge-discussions        | 1.4.1   |        |
| fof-follow-tags              | 1.2.7   |        |
| fof-drafts                   | 1.2.12  |        |
| fof-default-user-preferences | 1.2.1   |        |
| flarum-sticky                | v1.8.2  |        |
| flarum-statistics            | v1.8.1  |        |
| flarum-nicknames             | v1.8.2  |        |
| flarum-lock                  | v1.8.2  |        |
| flarum-likes                 | v1.8.1  |        |
| flarum-lang-english          | v1.8.0  |        |
| flarum-flags                 | v1.8.2  |        |
| flarum-emoji                 | v1.8.1  |        |
| blomstra-mark-unread         | 0.2.0   |        |
| askvortsov-rich-text         | v2.1.7  |        |
| askvortsov-markdown-tables   | v1.2.1  |        |
| askvortsov-categories        | v3.1.0  |        |
+------------------------------+---------+--------+
Base URL: https://forum.mylittlewordland.com
Installation path: [hidden]
Queue driver: sync
Session driver: file
Scheduler status: Never run
Mail driver: [hidden]
Debug mode: [hidden]

Possible Solution

No response

Additional Context

No response

[neoncube2]

It looks like this also happens with Chinese usernames, e.g. @大天犬木:

[neoncube2]

Another edge case: usernames that are email addresses can't be tagged, because they contain an @ symbol. For example, example@example.com can't be tagged.

[neoncube2]

Also, usernames with spaces. e.g. Hello World