Language Selector redirect is not working when language-specific Home URL is set

• Type: Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: 7.0.X, 7.1.X, 7.2.X, Master
• Fix Version/s: 7.0.0 DXP FP92, 7.0.10.14 DXP SP14, 7.0.X, 7.1.10 DXP FP18, 7.1.10.5 SP5, 7.1.X, 7.2.10 DXP FP5, 7.2.10.2 DXP SP2, 7.2.X, 7.3.1 CE GA2, 7.3.2 CE GA3, 7.3.10 DXP GA1, Master
• Component/s: WCM
• Labels:
  • ee-ts
  • liferay-dxp-70-sp14
  • liferay-dxp-71-sp5
  • liferay-dxp-72-sp2
  • liferay-fixpack-de-92-7010
  • liferay-fixpack-dxp-18-7110
  • liferay-fixpack-dxp-5-7210
• Branch Version/s:
  7.2.x, 7.1.x, 7.0.x
• Backported to Branch:
  Committed
• Fix Priority: 3
• Git Pull Request: https://github.com/brianchandotcom/liferay-portal/pull/84062

1. Set up and start a portal
2. Create a new site called 'customer'
3. Create a random page for it, to be able to access http://localhost:8080/web/customer
4. Place a Language Selector portlet onto it
5. Set the home URLs: Control Panel > Instance settings > Instance Configuration > General > Set Home URL + Default Logout Page + Default Landing Page to /es/web/customer
6. Open an incognito window and go to http://localhost:8080/ (this should show the Spanish version of the site)
7. Select another language in Language Selector (Selector de Idioma)

Expected result: no error thrown, the portal switches to the selected language
Actual result: Error page is shown, Exception in the logs:

2020-02-02 18:46:02.312 WARN  [http-nio-8080-exec-8][PortalImpl:6566] javax.servlet.ServletException: java.lang.StringIndexOutOfBoundsException: String index out of range: -2
javax.servlet.ServletException: java.lang.StringIndexOutOfBoundsException: String index out of range: -2
        at com.liferay.portal.struts.PortalRequestProcessor._process(PortalRequestProcessor.java:428)
        at com.liferay.portal.struts.PortalRequestProcessor.process(PortalRequestProcessor.java:155)
        at com.liferay.portal.internal.servlet.MainServlet.doGet(MainServlet.java:205)
...
        at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.StringIndexOutOfBoundsException: String index out of range: -2
        at java.lang.String.substring(String.java:1931)
        at com.liferay.portal.action.UpdateLanguageAction.execute(UpdateLanguageAction.java:121)
        at com.liferay.portal.struts.PortalRequestProcessor._process(PortalRequestProcessor.java:415)
        ... 92 more