If possible, i want to know the release planning date of 5.1.x line.

5.1 is really in maintenance mode. Right now there are not concrete plans to do another release. In your particular case there is an easy workaround by the way. Just add your own ValidationMessages.properties file to the root of your application/jar. In there you can fix the problematic messages by replacing value with validatedValue. You don't have to add all messages, just the ones you want to fix / are interested in. If a given message key is not found in the uyser specified bundle, Validator will always fall back to the built-in messages.