I have created a new language "en-JP" and used the below entry in LanguageDefinitions.config file
<language id="en" region="JP" codepage="65001" encoding="utf-8" charset="iso-8859-1" icon="flags/16x16/flag_Japan.PNG" />
But when I switch an item language in Sitecore CMS, it is throwing the below error.
Could you please suggest to me how we can add this language and I wanted to show en-JP in my url and based on context language we're also pulling search results. Hence it is not recommended to use any alternate language code apart from "en-jp"