Localization

Overleaf i18 Configuration

This document describes how to configure internationalization (i18n) for a self-hosted Overleaf instance.

Overleaf has been translated into multiple languages. With the appropriate configuration, you can:

• Run your Overleaf instance in a single fixed language, or
• Enable multiple languages, allowing users to switch languages dynamically, similar to www.overleaf.com.

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Single Language Configuration

The site language is configured using the environment variable OVERLEAF_SITE_LANGUAGE(or SHARELATEX_SITE_LANGUAGE for Overleaf versions 4.x and earlier).

Supported language codes include:

• en - English (default)
• es - Spanish
• pt - Portuguese
• de - German
• fr - French
• cs - Czech
• nl - Dutch
• sv - Swedish
• it - Italian
• tr - Turkish
• zh-CN - Chinese (simplified)
• no - Norwegian
• da - Danish
• ru - Russian
• ko - Korean
• ja - Japanese
• pl - Polish
• fi - Finnish

English is the default language. To change the interface language (for example, to Simplified Chinese), add the following line to config/variables.env:

config/variables.env

OVERLEAF_SITE_LANGUAGE=zh-CN

Then apply the configuration:

bin/up

After the services restart, the interface language in the web UI menus should reflect the new setting.

Multiple Language Configuration

To allow users to switch languages without logging out, your Overleaf instance must be configured to serve different languages based on domain names.

This section assumes:

• Your primary domain is overleaftest.com
• You have a wildcard TLS certificate (e.g. *.overleaftest.com)
• You are not using localhost (since it cannot support subdomain-based language routing)

For local testing, you may use a domain such as dev-overleaf.com.

1. TLS Proxy Configuration (Nginx)

   Your TLS reverse proxy must forward the original Host header so that Overleaf can determine which language domain the user accessed.

   Make sure the following directive is present:

   proxy_set_header Host $host;
   

   Here is an example Nginx configuration:

   server {
       listen 443 ssl;
       server_name    _; # Catch all, see http://nginx.org/en/docs/http/server_names.html
       server_name *.overleaftest.com;
       ssl_certificate /etc/nginx/ssl/nginx.crt;
       ssl_certificate_key /etc/nginx/ssl/nginx.key;
       ssl_protocols               TLSv1 TLSv1.1 TLSv1.2;
       ssl_prefer_server_ciphers   on;
       # used cloudflares ciphers https://github.com/cloudflare/sslconfig/blob/master/conf
       ssl_ciphers EECDH+CHACHA20:EECDH+AES128:RSA+AES128:EECDH+AES256:RSA+AES256:EECDH+3DES:RSA+3DES:!MD5;
   
       # config to enable HSTS(HTTP Strict Transport Security) https://developer.mozilla.org/en-US/docs/Security/HTTP_Strict_Transport_Security
       # to avoid ssl stripping https://en.wikipedia.org/wiki/SSL_stripping#SSL_stripping	
       add_header Strict-Transport-Security "max-age=31536000; includeSubdomains;";
       server_tokens off;
       add_header X-Frame-Options SAMEORIGIN;
       add_header X-Content-Type-Options nosniff;
       client_max_body_size 50M;
   
       location / {
           proxy_pass http://localhost:5000; # change to whatever host/port the docker container is listening on.
           proxy_set_header X-Forwarded-Proto $scheme;
           proxy_http_version 1.1;
           proxy_set_header Upgrade $http_upgrade;
           proxy_set_header Connection "upgrade";
           proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
           proxy_read_timeout 3m;
           proxy_send_timeout 3m;
           
           # add this to your nginx conf
           proxy_set_header Host $host;
       }
   }
   
2. Configure Cookie Domain

   To prevent users from being logged out when switching languages, cookies must be shared across language subdomains.

   Add the following line to config/variables.env:

   config/variables.env

   # Note the leading dot
   COOKIE_DOMAIN=.overleaftest.com
   

   This ensures that authentication cookies are valid for all subdomains under overleaftest.com.

3. Language–Domain Mapping

   Next, define how language codes map to subdomains using
   OVERLEAF_LANG_DOMAIN_MAPPING.

   Example Configuration

   config/variables.env

   OVERLEAF_LANG_DOMAIN_MAPPING='{"www": {"lngCode": "en","url": "https:\/\/www.overleaftest.com"},"cn": {"lngCode": "zh-CN","url": "https:\/\/cn.overleaftest.com"}}'
   

   With this configuration:

   • https://www.overleaftest.com → English interface
   • https://cn.overleaftest.com → Simplified Chinese interface

   You can extend this mapping with additional languages and subdomains as needed.

4. Redirect the Apex Domain

   Finally, redirect the apex domain (overleaftest.com) to the default language domain (www.overleaftest.com).

   server{
       listen 80;
       server_name overleaftest.com;
       return 301 https://www.overleaftest.com$request_uri;
   }
   
   server {
       listen 443 ssl http2;
       server_name overleaftest.com;
       ssl_certificate     /path/to/fullchain.cer;
       ssl_certificate_key /path/to/overleaftest.com.key;
       return 301 https://www.overleaftest.com$request_uri;
   }