Regional Indicator Symbols were introduced in 2010 in Unicode version 6.0,
based on the two-letter international code
and also added support for emoji and a limited number of national flags.
These symbols were badly named from the beginning, since they only support
Up to today, they are very badly supported by Unicode glyph engines,
but that has not stopped the Unicode consortium from evolving in version 10.0
from June 2017 the number of possible flags from 26x26 two-code-points
national codes to multi-code-points regional flags.
Given that even today, seven years later, country codes are almost always
simply displayed as two letters rather than as one, not daring to mention their
display as flags, I wouldn't expect the new standard to be implemented any faster.
If you are looking for a font that already supports the latest standards,
BabelStone Flags font,
which can be downloaded at the end of the linked article:
BabelStone Flags is a font that supports multicolour flag glyphs for Unicode character sequences representing various national, sub-national, supra-national, and miscellaneous flags. The current version of the font includes glyphs for 130 flags in total. At present the only Windows applications I use that fully support this font are Microsoft Word 2016 and the Firefox browser, although most other browsers (such as Chrome, Edge, and Internet Explorer) do partially support the colour glyphs in this font.
This font supports the two mechanisms for representing country and region flags described in the proposed update to Unicode Technical Standard #51 (Unicode Emoji): Regional Indicator Sequences and Flag Emoji Tag Sequences.