I am migrating struts from 2.3.35 to 2.5.17 version. Everything is working fine but special characters are displaying as ?. which are working with 2.3.35 version.
Is there any changes in 2.5.x version? please let me know.
There are many changes between Struts 2.3 and 2.5. The details are here. There is a migration guide here.
I'm not aware of any issues with special characters, but I can't think of any in our applications. There is a mention of New Locale Aware Conversion Logic in the migration guide which leads me to believe there may have been some internationalization changes. We would need some more information to properly diagnose your issue, however.