How to pass language for invoice text to "read_text" FM

Hello,

for invoice smartform, we need to print a text stored in invoice. Below is the screenshot. Pls advice which table stores the langauge for text in the invoice document. So that we can pick the language from that table/field and avoid hardcoding. Pls remember that one text can be created in many languages in the invoice document.

Pls see language as highlighted below. Lang is mandatory in READ _TEXT FM.

regards

sachin