localizedUnitName function
Returns a localized full name for a canonical unit symbol for the given
locale (base-locale fallback). Returns null when no mapping is found.
Implementation
String? localizedUnitName(String symbol, {String? locale}) {
if (locale == null || locale.isEmpty) return null;
final normalized = locale.toLowerCase();
final exact = _lookupInMaps(normalized, symbol);
if (exact != null) return exact;
final separatorIndex = normalized.indexOf(RegExp('[-_]'));
if (separatorIndex != -1) {
final base = normalized.substring(0, separatorIndex);
final baseMatch = _lookupInMaps(base, symbol);
if (baseMatch != null) return baseMatch;
}
return null;
}