Language customization performed by Studio generally redefine the entire $mod_strings instead of update just a single entry.
This way any customization implemented by extension, like new relationship, are missed.
So you should need to look at the custom/modules/<ModuleName>/language/en_us.lang.php.
Check if this script is redefining the entire $mod_strings. If yes, so you need to replace that by individual language entries.
For example:
old:
PHP Code:
$mod_strings = array(
'LBL_1' => 'Label 1',
'LBL_2' => 'Label 2',
'LBL_3' => 'Label 3',
);
new:
PHP Code:
$mod_strings['LBL_1'] = 'Label 1';
$mod_strings['LBL_2'] = 'Label 2';
$mod_strings['LBL_3'] = 'Label 3';
Then go to Admin -> Repair -> Rebuild Extensions
Cheers
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