The numeral field formatter that currently exists in Kibana makes heavy use of numeral.js and the numeral.js format strings. Those are not very intuitive to users and we often see that there are several misunderstandings around then, e.g. that the period and comma inside the string do not actually represent whether you want to use a comma or period as thousand separator, but where it's placed. Also it only allows one locale to be used per Space, making it impossible to use different number locales on different index patterns or fields. The following comment has more issues listed.

Same as for currencies (#25993) we should create a new better numeral field formatter.
The numeral field formatter should allow you to select the following configuration parameters:

• Thousand separator character
• Decimal point character
• Amount of decimal digits shown
• Whether the sign should also be shown for positive numbers
• Suffix/Prefix appended to the number
• Whether Large numbers should be shortened (e.g. 3M, 3k, etc.)

We should have some common templates to preselect at least the first two in that list with e.g. US numberal format, or other common formats used.

Since the Numer.js library is pretty much dead right now (and we're already maintaining a separate fork), it would be good if we would try not to use it anymore.

Since the currency is just a prefix/suffix to the number, maybe we don't want to build the separate currency field formatter (#25993) but instead merge both into one.