Custom Error Messages & Button Text
The Customer Account Fields app allows you to customize most of the text that is shown to users. Visit the Settings tab to configure each message.
Validation Error Placeholders
When a field fails your custom validation rules, you can specify the messaging. Note that the message is global for all errors of that type.
For example, if you specify that a field must contain a certain value, like "John", the default error message is: Value must contain "John". You can reword this to be something else, like "John is missing", using the following: @value is missing.