PolymerElements
Reconsider format.js as core dependency
Seems like the core libraries are not being maintained anymore and it doesn't look like yahoo is interested in keeping the project alive. Maybe it's time to move on to something else, like https://www.i18next.com/?
See https://github.com/yahoo/intl-messageformat/pull/156#issuecomment-312335055
It's now over a year since this issue was opened. We still rely on this, and the Polymer 3.0 release has just been made. But the situation with format.js seems to be unchanged, and it is still abandonware.
In addition to i18next, another possible option would be https://github.com/lingui/js-lingui . Linguijs is quite active and seems more polymer-ish than i18next. It is mainly focussed on react, where it replaces react-intl, which was also dependent on format.js. But the core is plain js.
No longer true: https://github.com/formatjs/formatjs/tree/master/packages/intl-messageformat
