I've just documented https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RelativeTimeFormat/resolvedOptions

The spec mentions "numberingSystem" and I see it added to the spec here https://github.com/tc39/proposal-intl-relative-time/pull/100

It doesn't seem to be added to our implementation yet.
PR for tests: https://github.com/tc39/test262/pull/2011

var de = new Intl.RelativeTimeFormat('de-DE');
de.resolvedOptions();
// Object { locale: "de-DE", style: "long", numeric: "always" }

Would have expected:
// Object { locale: "de-DE", style: "long", numeric: "always", numberingSystem: "latn" }

I have a patch for this bug, but as it currently requires a workaround for https://unicode-org.atlassian.net/browse/ICU-20280, it probably makes more sense to wait until bug 1533481 lands, because ICU-20280 has been fixed in ICU 64.

There's a r+ patch which didn't land and no activity in this bug for 2 weeks.
:anba, could you have a look please?
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Try: https://treeherder.mozilla.org/#/jobs?repo=try&selectedJob=255261545&revision=1eaf042f196531fe160fba5db9ac38287b1ce231

Pushed by nbeleuzu@mozilla.com:
https://hg.mozilla.org/integration/autoland/rev/e3ffa96d1b94
Add numberingSystem support to Intl.RelativeTimeFormat. r=jwalden

https://hg.mozilla.org/mozilla-central/rev/e3ffa96d1b94

Added to Fx 70 release notes: https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/70#JavaScript
Reference page: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RelativeTimeFormat/resolvedOptions
Compat data: https://github.com/mdn/browser-compat-data/pull/4870

Rather small change; no review needed. Let me know if you have feedback.

(In reply to Florian Scholz [:fscholz] (MDN) from comment #8)

Added to Fx 70 release notes: https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/70#JavaScript

The release notes should probably also mention that the Unicode extension key "nu" is now supported for the Intl.RelativeTimeFormat constructor.

For example before this bug new Intl.RelativeTimeFormat("th-u-nu-thai").format(123, "days") returned "ในอีก 123 วัน", but now the return value is "ในอีก ๑๒๓ วัน".

Updated the text on the release notes. Thank you!