MultiTerm Online itself does not have any Java requirements per se. It primarily needs the Apache Tomcat Web Server to host the MultiTerm Online instance. The Apache Web Server is indeed based on Java (to be able to function and operate) and that is where the need of using Java arises.
While RWS supports the MultiTerm Online tool, the question if RWS supports certain Java versions is responded below:
If Apache supports\tests and validates versions of Java for Tomcat, then we can assume that these will also work when deployed for MultiTerm Online. As an alternative to use Java Runtime (JRE) you can switch to open source Java/JDK or even Java Development Kit (JDK) under GPL (JDK12). Back in 2019, Apache announced support of JDK 12 for Tomcat, so that is also an option.
And our technical experts (Professional Services team) have configured installations with JDK13 and that worked too.