Nginx reverse proxy with dynamic basehref?

I have built an i18n app with Angular 9. My api is proxied with the /api/ url. But since i added i18n, proxy doesnt work anymore.
Rq: (Angular add /fr/ or /en/ to the url because i add –baseHref flag on compilation)

I want to know how can i tell to my proxy to add the dynamic basehref of my app to the proxy url ?
Exemple : How to transform GET to GET ?

So i have this nginx configuration :

location /fr/ { 
      autoindex on;
      try_files $uri$args $uri$args/ /fr/index.html;

  location /en/ {
      autoindex on;
      try_files $uri$args $uri$args/ /en/index.html;

  # Default to FR
  location / {
      # Autoindex is disabled here + the $uri$args/ is missing from try_files
      try_files $uri$args /fr/index.html;

# Proxy to API call
  location */api/ {
    proxy_pass http://rest-api:9000;

I’m trying to listen everythin before /api/ but this doesnt work…

Source: Angular Questions