PHP Check Url and print default parameters

I Have Url structure for multi language system like this:

for default language ie: en (not show/detect short language in url)

localhost/cms

localhost/cms/article/slug/etc...

And Another Language Like:

localhost/cms/fr

localhost/cms/fr/article/slug/etc...

My Idea:

1. define a list of available languages for My app,
2. define a default language I use when, a. there is no language provided (localhost/cms/users), b. the provided language is unknown (localhost/cms/fr/users).
3. in my code, get the current Language (ex: en) and the routableURI, a URI without any language in it (ex: cms/users)

I have This code:

function urlss(){

    $uri = $_SERVER['REQUEST_URI'];

    $languages = ['en', 'fr', 'es', 'de'];

    // this is my default language
    $defaultLang = 'en';

    // $currentLang is the language I'll use to show the contents
    $currentLang = $defaultLang;

    $uri = ltrim(rawurldecode($uri), '/');
    $parts = explode('/', $uri);

    if( ! empty($parts) && in_array(strtolower($parts[0]), $languages)) {
        $currentLang = array_shift($parts);
    }

    $routableUri = implode('/', $parts);

return $routableUri;

} 

My code output default language: (false Output)and not worked

check: localhost/cms/ Or localhost/cms/users/

Output is: cms/ Or cms/users/

Output for another language: (true Output)worked true

check: localhost/cms/fr/ Output is cms/fr/ Or localhost/cms/fr/users/Output is : cms/fr/users/

How do can i print my default language, without add/detect short language name in url like this?!

Check: localhost/cms Output Is:cms/en Or Check localhost/cms/users/ Output Is: cms/en/users/.