Text becomes illegible after Jar is created

I am working on a website. Am using angular, and java spring boot. The website contains different types of text characters (russian, french, etc) which are read from json files on the backend. If I start the site from the SpringBootApp main method it runs fine. However, once I generate the app for deployment into a JAR the foreign characters become illegible. This is happens either locally or remotely on a hosting platform. Any help will be appreciated.