Add language translation guidelines (#6639)

* Add language translation guidelines

* fix: minor formatting fix

---------

Co-authored-by: Prateek Shourya <prateekshourya29@gmail.com>

CONTRIBUTING.md

@@ -62,17 +62,143 @@ To ensure consistency throughout the source code, please keep these rules in min
 - All features or bug fixes must be tested by one or more specs (unit-tests).
 - We use [Eslint default rule guide](https://eslint.org/docs/rules/), with minor changes. An automated formatter is available using prettier.
 
-## Need help? Questions and suggestions
-
-Questions, suggestions, and thoughts are most welcome. We can also be reached in our [Discord Server](https://discord.com/invite/A92xrEGCge).
-
 ## Ways to contribute
 
 - Try Plane Cloud and the self hosting platform and give feedback
 - Add new integrations
+- Add or update translations
 - Help with open [issues](https://github.com/makeplane/plane/issues) or [create your own](https://github.com/makeplane/plane/issues/new/choose)
 - Share your thoughts and suggestions with us
 - Help create tutorials and blog posts
 - Request a feature by submitting a proposal
 - Report a bug
 - **Improve documentation** - fix incomplete or missing [docs](https://docs.plane.so/), bad wording, examples or explanations.
+
+## Contributing to language support
+This guide is designed to help contributors understand how to add or update translations in the application. 
+
+### Understanding translation structure
+
+#### File organization
+Translations are organized by language in the locales directory. Each language has its own folder containing JSON files for translations. Here's how it looks:
+
+```
+packages/i18n/src/locales/
+    ├── en/
+    │   ├── core.json       # Critical translations
+    │   └── translations.json
+    ├── fr/
+    │   └── translations.json
+    └── [language]/
+        └── translations.json   
+```
+#### Nested structure
+To keep translations organized, we use a nested structure for keys. This makes it easier to manage and locate specific translations. For example:
+
+```json
+{
+  "issue": {
+    "label": "Work item",
+    "title": {
+      "label": "Work item title"
+    }
+  }
+}
+```
+
+### Translation formatting guide
+We use [IntlMessageFormat](https://formatjs.github.io/docs/intl-messageformat/) to handle dynamic content, such as variables and pluralization. Here's how to format your translations:
+
+#### Examples
+- **Simple variables** 
+    ```json
+    {
+    "greeting": "Hello, {name}!"
+    }
+    ```
+
+- **Pluralization** 
+    ```json
+    {
+    "items": "{count, plural, one {Work item} other {Work items}}"
+    }
+    ```
+
+### Contributing guidelines
+
+#### Updating existing translations
+1. Locate the key in `locales/<language>/translations.json`.
+
+2. Update the value while ensuring the key structure remains intact.
+3. Preserve any existing ICU formats (e.g., variables, pluralization).
+
+#### Adding new translation keys
+1. When introducing a new key, ensure it is added to **all** language files, even if translations are not immediately available. Use English as a placeholder if needed.
+
+2. Keep the nesting structure consistent across all languages.
+
+3. If the new key requires dynamic content (e.g., variables or pluralization), ensure the ICU format is applied uniformly across all languages.
+
+### Adding new languages
+Adding a new language involves several steps to ensure it integrates seamlessly with the project. Follow these instructions carefully:
+
+1. **Update type definitions**  
+Add the new language to the TLanguage type in the language definitions file:
+
+    ```typescript
+    // types/language.ts
+    export type TLanguage = "en" | "fr" | "your-lang";
+    ``` 
+
+2. **Add language configuration**  
+Include the new language in the list of supported languages:
+
+    ```typescript
+    // constants/language.ts
+    export const SUPPORTED_LANGUAGES: ILanguageOption[] = [
+    { label: "English", value: "en" },
+    { label: "Your Language", value: "your-lang" }
+    ];
+    ```
+
+3. **Create translation files**  
+    1.  Create a new folder for your language under locales (e.g., `locales/your-lang/`).
+
+    2. Add a `translations.json` file inside the folder.
+
+    3. Copy the structure from an existing translation file and translate all keys.
+
+4. **Update import logic**  
+Modify the language import logic to include your new language:
+
+    ```typescript
+    private importLanguageFile(language: TLanguage): Promise<any> {
+    switch (language) {
+        case "your-lang":
+        return import("../locales/your-lang/translations.json");
+        // ...
+    }
+    }
+    ```
+
+### Quality checklist
+Before submitting your contribution, please ensure the following:
+
+- All translation keys exist in every language file.
+- Nested structures match across all language files.
+- ICU message formats are correctly implemented.
+- All languages load without errors in the application.
+- Dynamic values and pluralization work as expected.
+- There are no missing or untranslated keys.
+
+#### Pro tips
+- When in doubt, refer to the English translations for context.
+- Verify pluralization works with different numbers.
+- Ensure dynamic values (e.g., `{name}`) are correctly interpolated.
+- Double-check that nested key access paths are accurate.
+
+Happy translating! 🌍✨
+
+## Need help? Questions and suggestions
+
+Questions, suggestions, and thoughts are most welcome. We can also be reached in our [Discord Server](https://discord.com/invite/A92xrEGCge).