Custom Fields UI will not show unless 2 or more language packs are enabled

Summary

The Custom Fields UI Page at base_url/secure/admin/ViewCustomFields.jspa screenshot-1.png will not load unless 2 or more language packs are enabled.

Environment

• JIRA Core 7.12.0
• Reproducible on fresh installation.

Steps to Reproduce

1. Install JIRA Core 7.12.0
2. Create one or more custom fields.
3. Navigate to "Manage Add-ons".
4. Disable all languages, except English (United States) Language Pack screenshot-2.png.
5. Navigate to Custom Fields UI.

Expected Results

Custom Fields will load.

Actual Results

No Custom Fields can be seen. It seems that the page does not complete loading. screenshot-1.png

Notes

It seems that JIRA require 2 or more language packs to be enabled. Enabling any two languages, screenshot-3.png, would allow the Custom Fields UI to load screenshot-4.png

Workaround

Enable two or more language packs.