To reproduce:
1. Open attached project
2. Build and run to Android device with IL2CPP background
3. Connect the phone to editor console
4. Press the button in the application
5. Check console

Actual result: The CultureInfo.DateTimeFormat.DayNames returns the 8th weekday with an empty name
Expected result: The CultureInfo.DateTimeFormat.DayNames should return the 7 weekdays

Reproduced with: 2018.4.10f1; 2020.1.0a7
Can't check on 2017.4 due to errors.

Tested with:
VLNQA00010, Samsung Galaxy S8 (SM-G950U), Android 7.0, CPU: Snapdragon 835 MSM8998, GPU: Adreno (TM) 540
VLNQA00264, Samsung Galaxy S10+ (SM-G975F), Android 9, CPU: Exynos 9 9820, GPU: Mali-G76
VLNQA00166, Huawei P20 (EML-L29), Android 8.1.0, CPU: HiSilicon Kirin 970, GPU: Mali-G72
iPhone X iOS 11.3.1

Note: Does not reproduce on Editor, Standalone, Android with Mono Backend
Note: Logcat attached