validateLangCode function

String validateLangCode(String code)

Validates the given code as a supported language code.

Converts code to lowercase and checks if it exists in supportedLangCodes. If the code is invalid, an Exception is thrown with a helpful error message.

Example:

final lang = validateLangCode('Ne'); // returns 'ne'
validateLangCode('xx'); // throws Exception

code: The language code to validate (case-insensitive).

Returns the normalized (lowercase) version of the code if valid.

Throws Exception if the code is not supported.

Implementation

String validateLangCode(String code) {
  final normalized = code.toLowerCase();
  if (!supportedLangCodes.contains(normalized)) {
    throw Exception("❌ Unsupported language code: '$code'. "
        "Please use a valid ISO-639 code (e.g. 'ne' for Nepali, 'fr' for French).");
  }
  return normalized;
}