Wordpress - wpml different domains - behind reverse proxy

Question

Situation

My client has a webshop in 2 languages:
- my-website.be (Dutch + French)
- my-website.nl (Dutch)

I have to remake the /blog for these 3 languages using Wordpress.
I have no access to the main website and server, so this has to be done with reverse proxy.

Ideally this will look like this:
- my-website.be/nl-be/blog/%postname%/
- my-website.be/fr-be/blog/%postname%/
- my-website.nl/blog/%postname%/

We use WPML(pro) for translation on the website
I have to proof this is possible

The problem

I'm trying to proof this is possible with wpml + reverse proxy on my local machine using MampPro for Windows. (As I do not have real/live servers/domains available to test this) And this is not working correctly whatever I try.

The local test setup

• Made 2 local servers for reverse proxy:
  • my-site.localbe
  • my-site.localnl
• Made 1 local server for the blog: my-site.test
• Set the .htaccess files in the 2 proxy domains to reverse proxy this:

my-site.localbe

<IfModule mod_rewrite.c>
    RewriteEngine On  
    RewriteRule ^nl-be/blog/(.*)$ http://my-site.test/$1 [P]  
    RewriteRule ^fr-be/blog/(.*)$ http://my-site.test/$1 [P]  
</IfModule>

my-site.localnl

<IfModule mod_rewrite.c>
    RewriteEngine On  
    RewriteRule ^blog/(.*)$ http://my-site.test/$1 [P]  
</IfModule>

• Setup 3 languages in WPML (nl-be, fr-be, nl-nl)
• Set the Wordpress site url to the default http://my-site.test

==> with this setup both reverse proxy domain just show the default homepage and/or subpages. There's no way to access the other languages.

What we've tried

• Changing Wordpress wp_home and wp_siteurl to:
  /nl-be/blog (as nl-be is set as the default language in wpml)
• Setting up wpml as "different domain for each language", but that places /nl-be/ hardcoded after each of those different domains.
  (with wp_home and wp_siteurl set as my-site.test)
• Fiddling with proxypass settings in .htaccess (probably wrong)
• Changing the wpml language domains hardcoded in database

• Overwriting the server_name variable in functions.php as follows:

  $_SERVER['SERVER_NAME'] = $_SERVER['HTTP_X_FORWARDED_HOST'];
  

• Combinations and variations off all above.

Results

• Mostly error 500
• A broken .htaccess when saving permalinks
• To much internal redirections
• Links looking like my-site.testbe/nl-be/blog/nl-be/*
• Styling and scripts loading from wrong domain
• Combinations of all above

I would like to know

• if this setup is even possible (local or on real linux servers)
• if the mistake is in my reverse proxy / htaccess part
• if the mistake is in configuring wordpress and wpml
• any information that can help me solving this.

Thanks a lot, a developer in distress