How to add custom strings based on plug-ins

Hi,
you need first to declare your new string using the pll_register_string function:
pll_register_string(‘group’, ‘string-name’);

And integrate it where you want to see it displayed in your theme, using the pll_e function:
pll_e(‘string-name’,’group’);

For instance:
In my functions.php:
if (function_exists(‘pll_register_string’)) {
pll_register_string(‘wpnotification’, ‘message’);
}

and in my header.php
pll_e(‘message’,’wpnotification’);

in wordpress admin (language -> strings translation):
English: “my message in english”
French: “my message in french”

Great , it worked excellent.