This sessions example looks at internationalisation (i18n) using the JSTL internationalisation library.
See supporting video internationalisation - i18n
https://docs.oracle.com/javaee/5/tutorial/doc/bnakw.html Internationalisation Tag Library
https://phrase.com/blog/posts/internationalization-basic-jsp-servlet/ Internationalisation Tag Library tutorial
There are two examples, one using simple JSP's and one using spring boot
The spring boot example ports the simple example as both plane JSPs and JSPs using Spring MVC
You should be able to migrate this technology into your main application.