Partial answer

According to https://en.wikipedia.org/wiki/Date_format_by_country, the following locales use YMD date format:

Afghanistan, Albania, Bangladesh, Cambodia, Canada, China, People's Republic of, Denmark, Germany, Hong Kong, Hungary, Iran, Japan, Kenya, Korea, Latvia, Lithuania, Macau, Mongolia, Myanmar, Namibia, Nepal, Norway, Singapore, Slovenia, South Africa, Sri Lanka, Sweden, Taiwan,Republic of China, United Kingdom, United States of America

Notes

I didn't find a simple table that combines the date format and currency symbol but find the following that could help

• https://en.wikipedia.org/wiki/Date_format_by_country
• https://en.wikipedia.org/wiki/Currency_symbol

Other interesting findings

Spefications / open source projects

Google participates in the below projects, so is very likely that Google Sheets use them

• http://cldr.unicode.org/

The Unicode CLDR provides key building blocks for software to support the world's languages, with the largest and most extensive standard repository of locale data available. This data is used by a wide spectrum of companies for their software internationalization and localization, adapting software to the conventions of different languages for such common software tasks

• http://site.icu-project.org/

ICU is a mature, widely used set of C/C++ and Java libraries providing Unicode and Globalization support for software applications. ICU is widely portable and gives applications the same results on all platforms and between C/C++ and Java software.

Tools

• http://demo.icu-project.org/icu-bin/locexp

This demo illustrates the International Components for Unicode localization data. The data covers two hundred five different languages, further divided into four hundred eighty-eight regions and variants. For each language, data such as days of the week, months, and their abbreviations are defined.