number.toLocaleString(locale) doesn't work as expected

### Problem description

The given locale is not being applied.

### Environment

- Tabris.js version: 2.6.1
- OS: API 28

### Code snippet

```javascript
console.log(1923489123441.12.toLocaleString('de-DE'));

// Output Android:
// 1923489123441.12

// Output iOS (expected):
// 1.923.489.123.441,12
```