If I try to edit a date in the Data tab of a Goal, there is no calendar widget.
On a related note, it would be nice have proper (human formed) date formats in the interface, e.g. 3/Nov/2016 (and equivalent for Americans or other regions) as opposed to the machine Y-m-d format 
I disagree. Y-m-d is my strongly preferred format in all contexts.
that’s why programmers have invented user preferences 
Right. But having too many preferences is considered harmful. It wastes people’s time making too many choices, and it makes the code complex (and likely to have bugs) with the combinatorial explosion of possibilities.
On this particular topic, I’m actually a little surprised localization isn’t supported at the browser level. Having one choice for what date format you want to see, and then having every website respect that, seems a lot better to me than every website having to individually decide whether to support this.
Pretty much every web platform that considers itself serious towards an international audience gives users regional settings for dates, distances, etc. Take for example all the fitness-related web sites/apps (MFP, Garmin, Strava, etc) that Beeminder connects and depends on (and would like to capture users from).
It’s not like I’m suggesting a preference over colours or having 3 vs 4 columns on the gallery page… 
I do feel pretty strongly about Y-M-D format. 
I use it too a lot for naming files that need to be sorted. But not on user interfaces for my clients
I suspect that there’s a lot more pressing UVIs and features to be built first.
In terms of internationalisation, I also suspect that pledging in local currency is a more common desire than seeing dates in local formats.
Shall we park this against the day that we aim to have a multi-lingual interface?
Surely this is an easy UVI given that almost all other date fields in the new interface have a calendar widget attached
Bumping this
Given that date field in the Commitment tab has a calendar widget (and so do the X-min/max fields in Graph Settings), I fail to see any reason the Data tab can’t have one…
@dreev that’s an easy UVI for your buffer