Uncaught Error: Call to undefined function pll_e()

Hi there! I have a custom made module and I’ve tried to translate some parts from it.

So I’ve reguistered the string in the plugin php file:

add_action(‘init’, function() {
pll_register_string(‘somename’, ‘The name of the string’);
});

I’ve used in the template:
<?php pll_e(‘The name of the string’) ?>

but then I get:

Uncaught Error: Call to undefined function pll_e() on the page.
I guess I am missing something, that I have to include a file or call another function.
I have also tried to register the function in the functions.php of the theme, but I get the same result.