Use ISO dates all over

I try to avoid using localized date formats to avoid misunderstanding, so I would like Libreoffice to use ISO format for dates where ever possible.

Most crucial to me is the value field in LibreCalc. In the cells, I can adjust with Format Cells, but how do I tell LibreCalc that I also want the value in the field to be in ISO-format (e.g. so I can press F2 and edit an ISO formatted date)?

Sure I’m missing something, but with version, if a cell format is AAAA-MM-DD, with F2 edits with that format, and entering a value like 2016-12-20 in any cell is accepted and the cell is formatted AAAA-MM-DD.
(My locale is Spanish and my date acceptance pattern ‘D/M/Y;D/M’

(Sorry. I had screwed up different things. Used day?)