firefly-iii/resources/lang/en/firefly.php

<?php
return [
    'test'            => 'You have selected English.',
    'welcome'         => 'Welcome to Firefly!',
    'close'           => 'Close',
    'pleaseHold'      => 'Please hold...',
    'mandatoryFields' => 'Mandatory fields',
    'optionalFields'  => 'Optional fields',
    'options'         => 'Options',
    'something'       => 'Something!'

];