american english - Numerical decades: change to s or ies?

As a native (American) English speaker, I change written decades to their numerical forms like the following:
Eighties = 80s, nineties = 90s

Throughout my time on the internet, though, I have seen a lot of second-language English speakers write decades ending in ies, like so:
Eighties = 80ies, nineties = 90ies

Is there any reason that this should be preferred?

Answer

The common way to refer to decades is to add an “s” without apostrophe. Though the are usage instances of -ies suffixes after numbers to indicate decades, you should probably avoid it.

Decades:

No apostrophe is required with the ‘s’ for decades when listed in full (e.g. 1990s). In situations where just the decade is indicated (e.g. ’80s) the direction of the leading apostrophe indicates that information ahead of the number “80” has been removed (i.e. it is a contraction of 1980 in this instance).

1990s,
1840s,
’80s

(Writing Style Guide)