php - Multiple languages + Htaccess

I need for a domain to manage languages (en/it/pt/es) plus remove www. and force https

    RewriteEngine On
    # -> www.example.com to example.com
    RewriteCond %{HTTP_HOST} www.example.com
    RewriteRule (.*) http://example.com/$1 [L,R=301]

    # -> http -> https
    RewriteCond %{SERVER_PORT} 80
    RewriteRule (.*) https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301] 

I don't know how to make this rewrite rule :
index.php?lg=es -> /es/ and not /es or /es.php and even refuse index.php?lg=es

RewriteRule ^([a-zA-Z0-9]+)/?$ index.php?lg=$1

??

The SEO is bad for my website only english is known by engine and others languages are on the 4th page of result..

Is it the reason why because i've got two ways to display url ??

example.com/it/ and example.com/it should not return the same page

Thanks for help.

EDIT (i think all is correct ?? ) : 07 October thanks for all answers :

      RewriteEngine On
      RewriteCond %{HTTP_HOST} ^www.example.com$ [OR]
      RewriteCond %{SERVER_PORT} 80 [OR]
      RewriteCond %{HTTPS} off
      RewriteRule ^(.*)$ https://example.com/$1 [R=301,L]
      RewriteRule ^/?([a-z]{2})$ /$1/ [R=301,NC,L]
      RewriteRule ^/?([a-z]{2})/$ /index.php?lg=$1 [NC]

      RewriteCond %{ENV:REDIRECT_STATUS} ^$
      RewriteCond %{REQUEST_URI} ^/?index.php$
      RewriteCond %{QUERY_STRING} ^lg=([^&]+)(&.*)?$
      RewriteRule ^/?index.php$ - [F]
     ErrorDocument 404 /404.php

Just a question : Is testing if https off really useful (slow connection ?) ? thanks

EDIT 8 February 2018

After months of use there are a lot of 404 errors .
Htaccess need to more simplified.

I just need :

 1) www -> non-www
 2) http -> https
 3) index.php -> example.com
 4) redirect index.php?lg=it and index.php?lg=es and index.php?lg=pt 

    to example.com/it or to example.com/es or to example.com/pt

and if it's not one of this language -> go to homepage example.com or 404 ?? but Google webmaster will increase 404 error ...

I need a very simplify version of htaccess with 3 languages with Rewrite Base in it ? or not ?

here is my htaccess :

RewriteEngine On

RewriteCond %{HTTP_HOST} ^www.example.com$ [OR]
RewriteCond %{SERVER_PORT} 80 [OR]
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://example.com/$1 [R=301,L]
RewriteRule ^/?([a-z]{2})$ /$1/ [R=301,NC,L]
RewriteRule ^/?([a-z]{2})/$ /index.php?lg=$1 [NC]
RewriteCond %{ENV:REDIRECT_STATUS} ^$
RewriteCond %{REQUEST_URI} ^/?index.php$
RewriteCond %{QUERY_STRING} ^lg=([^&]+)(&.*)?$
RewriteRule ^/?index.php$ - [F]

ErrorDocument 404 /404.php

Everything is managed in the index.php, is it better to create 3 pages ?

index.php -> redirect to example.com

es.php -> redirect to example.com/es

it.php -> redirect to example.com/it removing .php

Can someone make it ? Thanks

Answer

This should work for you as accepted:

RewriteEngine On
# redirect to none-www and https
# if host do not starts with www.
RewriteCond %{HTTP_HOST} ^www\.(([A-Za-z0-9][A-Za-z0-9-]+\.)+[A-Za-z]{2,})$ [OR]
# or if Port is 80

RewriteCond %{SERVER_PORT} 80 [OR]
# or if https is off
RewriteCond %{HTTPS} off
# redirect to example.com with https
RewriteRule ^(.*)$ https://%1/$1 [R=301,L]

# Redirect Language Strings without Trailing Slashes 
RewriteRule ^/?([a-z]{2})$ /$1/ [R=301,NC,L]

# Rewrite Language string

RewriteRule ^/?([a-z]{2})/$ /index.php?lg=$1 [NC]

# Prevent direct access to /index.php?lg=$1 [QSA,NC,L]
RewriteCond %{ENV:REDIRECT_STATUS} ^$
RewriteCond %{REQUEST_URI} ^/?index.php$
RewriteCond %{QUERY_STRING} ^lg=([^&]+)(&.*)?$
RewriteRule ^/?index.php$ - [F]

I tested this positive an Ubuntu 16.04.03 LTS with Apache 2.4.27