183 use kc settings for language selection settings

[lukasmatusiewicz]

This PR includes several changes aimed at improving internationalization support, simplifying code, and enhancing error handling in the privacyidea-authenticator. The most important changes include the removal of hardcoded language strings, the addition of new localized messages, and minor code simplifications.

Internationalization Improvements:

• Added new localized messages to messages_de.properties, messages_en.properties, messages_fr.properties, and messages_pl.properties files for better support of different languages. [1] [2] [3] [4]
• Removed hardcoded language strings from Const.java and PrivacyIDEAAuthenticator.java and replaced them with configuration-based messages. [1] [2]

Code Simplifications:

• Removed unused constants from Const.java to clean up the codebase. [1] [2] [3]
• Simplified the PrivacyIDEAAuthenticator.java by removing redundant language handling code and improving error message formatting. [1] [2] [3] [4] [5] [6]

Error Handling Enhancements:

• Improved error logging in JavaScript files by using localized error messages instead of hardcoded strings. [1] [2] [3]

Template Updates:

• Updated privacyIDEA.ftl template to use localized messages for various UI elements, improving the user experience for non-English speakers.

Miscellaneous:

• Updated the subproject commit reference in java-client.