apache splunk "Invalid language specified" issue

[erictse2]

Hi,

I configure an apache site
https://dev-dit.th.gov.bc.ca/en-US/app/cars_events/event_summary_html

I got

"Invalid language specified" issue

Here is the two lines in apache config

RewriteRule ^/en-GB/app/cars_events/(.*)$ http://dev-dit-reports.th.gov.bc. ca:8000/$1 [P,L,NC]
ProxyPassReverse /en-GB/app/cars_events/ http://dev-dit-reports.th.gov.bc.ca:8000/en-GB/app/cars_events/

If I hit the site directly I don't have problems

http://dev-dit-reports.th.gov.bc.ca:8000/en-US/app/cars_events/event_summary_html

Have I done something wrong?
Is it problem on our side?
What should I do as next steps?

Thanks and regards,