Wrong locale time in Android webview

We have an android app which more or less constists of only a webview, displaying a webapp. At some point, we want to display some timestamp to the user and use the following code

let dateString = new Date().toLocaleTimeString();

The problem is, this always produces a 12h time representation (ie with AM/PM, for instance 3:15 PM instead of 15:15), even if we set the device to use 24h clock (and the device does respect this setting, because we see the correct time in the statusbar). We also set the device to use German language and removed the english language settings. No luck either. The device locale is used, as our app is shown in the correct language, but the timestrings are still wrong.

window.navigator.language  -> "de-AT"
new Date().toLocaleTimeString(); -> "6:10:13 PM"
new Date().toLocaleTimeString(window.navigator.language); -> "18:10:32"

At a first glance, the last line seemed as a possible workaround, but if language is for instance "en-US" this will always return 12h format, regardless whether the os is configured for using 24h clock or not.

I'm aware of this question, which seems somehow related to this issue, but the answers don't work for us.

Using various virtual devices I found out, it still works correctly on chrome 58 (on API 26) but does not work any more on chrome 61 (on API 27). Currently testing at chrome 70 beta, the problem still persists.

It's also important to note, that it works correctly in chrome itself (ie if I display a time stamp in a test website, it uses the system settings), but only fails in the webview.

Our current workaround is to generate timestamps via native app, but that seems rather clumsy.

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