Strings Problem inside external JS/CSS file

/*
 * Problems: Some strings set in external js and CSS file, therefore we *couldn't* directly use lang() methods inside
 * Troubleshoot proposal: see below
 */

// Proposal for strings in JS:

<html>
...

// jQuery
<script type="text/javascript" defer="defer" src="https://yukbisnis.com/applications/assets/js/jquery.js"></script>

// Define currently set language with php methods "get_language()", then use the variable to dynamically load
// javascript function inside the external js file
<script>var used_lang = '<?php get_language(); ?>'</script>

// All JavaScripts
<script>...</script>
<script>...</script>
<script>...</script>

...
</html>


// =====================================================================================================================


// Proposal for strings in CSS (option 1):
// * internal CSS

<html>
    <head>
        ...
        <style>
            #the_id::after {
                content: "<?= lang('STRING_KEYWORD'); ?>" ;
            }
        </style>
    </head>
    <body>
        ...
    </body>
</html>

// Proposal for strings in CSS (option 2, may be not good idea):
// using php methods to dynamically load which stylesheet file to be loaded. i.e:
// <link media="all" rel="stylesheet" type="text/css" href="https://yukbisnis.com/.../<?php echo (get_lang() === 'en') ?  'en_style.css' : 'id_style.css'; ?>" />