Documentation: 🌍 Add More Languages & Expand Translation Coverage

## Goal

Extend the app's multilanguage support beyond English and German. Add new languages and complete translation coverage for all screens and features.

## Current State

**full translation**
- ✅ English — full coverage (default)

## Wanted Languages

Priority languages:

- [x] Spanish (`values-es`) Thanks! https://github.com/Ferinjoque
- [x] Chinese Simplified (`values-zh-rCN`) Thanks! https://github.com/Dawn3901
- [ ] French (`values-fr`)
- [ ] Portuguese (`values-pt`)
- [ ] Russian (`values-ru`)
- [ ] Japanese (`values-ja`)
- [ ] Arabic (`values-ar`)
- [ ] Hindi (`values-hi`)
- [ ] Korean (`values-ko`)
- [ ] Italian (`values-it`)
- [ ] Turkish (`values-tr`)
- [ ] Dutch (`values-nl`)
- [ ] Polish (`values-pl`)
- [ ] Indonesian (`values-in`)
- [ ] Vietnamese (`values-vi`)
- [ ] Thai (`values-th`)
- [ ] Ukrainian (`values-uk`)
- [ ] Chinese Traditional (`values-zh-rTW`)
- [ ] Czech (`values-cs`)
- [ ] Greek (`values-el`)
- [ ] Swedish (`values-sv`)
- [ ] Norwegian (`values-no`)
- [ ] Danish (`values-da`)
- [ ] Finnish (`values-fi`)

Other languages welcome!

## Tasks

### Translation Work
- [ ] Complete existing translations (100% coverage)
- [ ] Create string resource files for new languages
- [ ] Translate all UI strings, error messages, and tooltips
- [ ] Review translations for aviation/technical terminology accuracy

### Code Improvements
- [ ] Audit codebase for hardcoded strings → move to `strings.xml`
- [ ] Add new language to selection in SettingsMenu.kt

### Documentation (example /docs/EN/ )
- [ ] Create translation guide for contributors
- [ ] Document aviation-specific terms that need consistent translation

## How to Contribute

1. Pick a language you're fluent in
2. Copy `res/values/strings.xml` to `res/values-XX/strings.xml`
3. Translate all strings (keep the `name` attributes unchanged)
4. Submit a PR with your translations
5. Native speakers welcome for review!

## String File Location

```
app/src/main/res/
├── values/
│ └── strings.xml # English (default)
├── values-de/
│ └── strings.xml # German
├── values-fr/
│ └── strings.xml # French (to be added)
└── ...
```

## Notes

- Keep translations concise (UI space is limited on mobile)
- Aviation terms should match standard terminology in each language
- When unsure, add a comment in the PR for discussion

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