operator == method
Whether other is a language with the same isoCode, ignoring case.
name and nativeName are display data and take no part in equality.
So a Language('nb', 'Norwegian') kept from an older version of this
package still equals Languages.norwegianBokmal, whose name changed
in 0.4.0.
Implementation
@override
bool operator ==(Object other) =>
other is Language && isoCode.toLowerCase() == other.isoCode.toLowerCase();