feat: add i18n localization via i18next for 13 languages

TRANSLATORS.md

@@ -0,0 +1,87 @@
+# Translating XR Gaming Plugin
+
+Thank you for helping translate the XR Gaming Decky plugin! This guide explains how to contribute a translation.
+
+## Supported Languages
+
+| Code    | Language              | File                                     |
+|---------|-----------------------|------------------------------------------|
+| `en`    | English (base)        | `src/locales/en/translation.json`        |
+| `de`    | German                | `src/locales/de/translation.json`        |
+| `es`    | Spanish               | `src/locales/es/translation.json`        |
+| `fr`    | French                | `src/locales/fr/translation.json`        |
+| `it`    | Italian               | `src/locales/it/translation.json`        |
+| `ja`    | Japanese              | `src/locales/ja/translation.json`        |
+| `zh-CN` | Simplified Chinese    | `src/locales/zh-CN/translation.json`     |
+| `ru`    | Russian               | `src/locales/ru/translation.json`        |
+| `ko`    | Korean                | `src/locales/ko/translation.json`        |
+| `pt-BR` | Portuguese (Brazil)   | `src/locales/pt-BR/translation.json`     |
+| `pl`    | Polish                | `src/locales/pl/translation.json`        |
+| `tr`    | Turkish               | `src/locales/tr/translation.json`        |
+| `zh-TW` | Traditional Chinese   | `src/locales/zh-TW/translation.json`     |
+
+## How to Contribute a Translation
+
+### 1. Open the English base file
+
+The English file at `src/locales/en/translation.json` contains all translatable strings organized by section. Use this as your reference for what each key means.
+
+### 2. Find your language file
+
+Open the file for your language (e.g., `src/locales/de/translation.json` for German). The file starts as an empty JSON object `{}`. Any key that is missing from your language file will automatically fall back to English.
+
+### 3. Add translations
+
+Copy keys from the English file into your language file and replace the English values with your translations. You do **not** need to translate every key — untranslated keys will fall back to English.
+
+**Example** — German partial translation:
+```json
+{
+  "device": {
+    "noDevice": "Kein Gerät verbunden",
+    "connected": "verbunden"
+  },
+  "button": {
+    "needHelp": "Hilfe benötigt?",
+    "showAdvanced": "Erweiterte Einstellungen anzeigen",
+    "hideAdvanced": "Erweiterte Einstellungen ausblenden"
+  }
+}
+```
+
+### 4. Important rules
+
+- **Keep the same JSON structure** (nested keys) as the English file.
+- **Do not translate key names** — only translate the values (strings on the right side of `:`).
+- **Preserve placeholders** like `{{time}}`, `{{count}}`, `{{units}}` — these are filled in at runtime with dynamic values. Translate the surrounding text but keep the `{{...}}` placeholders as-is.
+- **Preserve HTML tags** in strings that contain them (e.g., `<b>`, `<i>`) — these add formatting. Only translate the surrounding text.
+- **Do not change** special Unicode characters like `\u2011` (non-breaking hyphen) or `\u00a0` (non-breaking space) — keep them as-is.
+
+### 5. Submit your translation
+
+Open a pull request with your updated language file. Please test your translation if possible (see the Development section below).
+
+---
+
+## Adding a New Language
+
+If your language is not listed above:
+
+1. Create a new directory: `src/locales/<language-code>/`
+2. Create `src/locales/<language-code>/translation.json` starting with `{}`
+3. Add the import and resource entry in `src/i18n.ts`
+4. Open a pull request
+
+Use [BCP 47](https://www.ietf.org/rfc/bcp/bcp47.txt) language tags (e.g., `pt-BR`, `zh-TW`).
+
+---
+
+## Maintaining Translations (for maintainers)
+
+When new strings are added to the codebase:
+
+1. Add the new English string(s) to `src/locales/en/translation.json` under the appropriate section.
+2. Open an issue or PR noting which keys were added so translators can update their files.
+3. Existing translations will continue to work — missing keys fall back to English automatically.
+
+No build step is needed for translation files themselves; they are bundled into the plugin at build time.

package.json

@@ -45,6 +45,7 @@
   },
   "dependencies": {
     "@decky/api": "^1.1.2",
+    "i18next": "^25.10.10",
     "qrcode.react": "^4.0.1",
     "react-icons": "^5.3.0"
   },