Originally brought up in #55535 by @jans-y

Many other languages have the same problem with manual date entering .
e.g.: cs, sk, hu -> they all use . (dots) not / (slash)

Switching to 'de' (German) solves the issue.

@darrenaustin also did some research and found that the following might be incorrect as well:

af: sep = /, help = dd-mm-jjjj
fr_CA: sep = /, help = jj-mm-aaaa
hy: sep = /, help = օօ.աա.տտտտ
nl: sep = /, help = dd-mm-jjjj

I'll file these change requests to the internal translation console for the translation teams to update as appropriate for the locales mentioned above.