Control Panel not being displayed when selecting locale with "-" in the URL

• Type: Regression Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: 7.0.X, 7.1.1 CE GA2, 7.1.10 DXP FP3, 7.1.10 DXP FP4, 7.1.X, Master
• Fix Version/s: 7.0.0 DXP FP76, 7.0.X, 7.1.10 DXP FP8, 7.1.X, Master
• Component/s: Control Panel Framework, Portal Services > Localization, WCM > Languages Portlet
• Labels:
  • QA-V
  • liferay-fixpack-de-76-7010
  • liferay-fixpack-dxp-8-7110
• Branch Version/s:
  7.1.x, 7.0.x
• Backported to Branch:
  Committed
• Story Points: 1
• Fix Priority: 3
• JDK:
  Oracle Sun JDK 8
• Application Servers:
  Apache Tomcat 9.0.x
• Browsers:
  Chrome (latest)
• Databases:
  MySQL 5.7
• Device Type:
  Desktop
• Sprint: U&SM - Sprint 9
• Git Pull Request: https://github.com/brianchandotcom/liferay-portal/pull/66506

After the change added by the issue https://issues.liferay.com/browse/LPS-78738 , when selecting a language that makes the URL to include a locale with a "-", like for example "en-GB", this breaks the Control Panel.

Steps to reproduce:

1. Set this property in portal-ext.properties: locale.prepend.friendly.url.style=2
2. Set this property in portal-ext.properties: locales.enabled=en_US,en_GB,nl_NL,nl_BE
3. Add a Language Selector widget to any page of a site
4. Select british english or belgian nederlands
5. Click on the menu link to access the Control Panel

Actual result:
The Control Panel is broken.

Expected result:
The Control Panel is displayed as usual.