Currently all the texts and messages appear in English. Can we change it as per user's preferences? It should cover all the messages like - "Invalid Email Address", "Submit", "Submit Another" etc.

Yes, the apps can be customized in several languages, but this involves configuration by the Clappia team and is not included as part of the platform's self-service.
As of the current scenario, app names and field labels support multiple languages as hard-coded text.