📝(i18n) describe process for translations

This explains the command to run to be able to translate our project.

docs/i18n.md

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+# Internationalization (i18n)
+
+The backend and the frontend of the application are internationalized.
+This means that the application can be translated into different languages. 
+The application is currently available in English and French.
+
+## Local setup
+
+To be able to upload/retrieve translation files to/from Crowdin you need to
+setup your local environment with the following environment variables:
+
+```bash
+cp ./env.d/development/crowdin.dist ./env.d/development/crowdin
+```
+
+Then fill in the `CROWDIN_API_TOKEN` and `CROWDIN_PROJECT_ID` variables in the
+`./env.d/development/crowdin` file.
+
+This configuration file will be loaded by the crowdin docker instance.
+
+
+## How to update the translations
+
+1/ Generate the translation files for both frontend and backend and upload them to the translation platform (crowdin):
+  ```bash
+  make i18n-generate-and-upload
+  ```
+
+2/ Fill the missing translations on the translation platform:
+  
+  => [https://crowdin.com/project/lasuite-people](https://crowdin.com/project/lasuite-people)  
+
+3/ Download the translated files from the translation platform and compile them:
+  ```bash
+  make i18n-download-and-compile
+  ```