contao-leaflet-maps/module/languages/en/leaflet_layer.php

<?php

$GLOBALS['TL_LANG']['leaflet_layer']['provider'][0] = 'Leaflet provider';
$GLOBALS['TL_LANG']['leaflet_layer']['provider'][1] = 'Leaflet tile provider';
$GLOBALS['TL_LANG']['leaflet_layer']['group'][0]    = 'Layer group';
$GLOBALS['TL_LANG']['leaflet_layer']['group'][1]    = 'Layers group';
$GLOBALS['TL_LANG']['leaflet_layer']['markers'][0]  = 'Markers';
$GLOBALS['TL_LANG']['leaflet_layer']['markers'][1]  = 'Marker collection';