Confirmed by my tests in tdf#158502.

But seems to work if there are parameters on the NatNum

[NatNum12 D=ordinal]\"D MMM\"
shows
"first Dec"
for a date in the cell 1/12/2023

(In reply to m.a.riosv from comment #2)
> But seems to work if there are parameters on the NatNum
> 
> [NatNum12 D=ordinal]\"D MMM\"
> shows
> "first Dec"
> for a date in the cell 1/12/2023

I'm sorry but I don't understand. What exact literal text is being added to that number format code?

OTOH, having the following format code seems to show the additional literal text correctly:

[NatNum12 D=ordinal]"Ending date: "\"D MMM\"

The problem is with things like:
[NatNum12 D=ordinal]"Total: "0

or with:

[NatNum12]"Total: "0.00

IOW, somehow the additional quotation marks are needed (as for text)
Total: "\"0.00\"

but I'm not sure that such code (or a similar one) would end up with the desired result to be displayed in each variant.

Confirmed.

Version: 7.6.3.1 (X86_64)
Build ID: 60(Build:1)
CPU threads: 8; OS: Linux 6.6; UI render: default; VCL: gtk3
Locale: es-MX (es_MX.UTF-8); UI: es-ES
Calc: threaded

(In reply to ady from comment #3)
> (In reply to m.a.riosv from comment #2)
> > But seems to work if there are parameters on the NatNum
> > 
> > [NatNum12 D=ordinal]\"D MMM\"
> > shows
> > "first Dec"
> > for a date in the cell 1/12/2023
> 
> I'm sorry but I don't understand. What exact literal text is being added to
> that number format code?
> 
> OTOH, having the following format code seems to show the additional literal
> text correctly:
> 
> [NatNum12 D=ordinal]"Ending date: "\"D MMM\"
> 
> The problem is with things like:
> [NatNum12 D=ordinal]"Total: "0
> 
> or with:
> 
> [NatNum12]"Total: "0.00
> 
> IOW, somehow the additional quotation marks are needed (as for text)
> Total: "\"0.00\"
> 
> but I'm not sure that such code (or a similar one) would end up with the
> desired result to be displayed in each variant.

Quotes, one more example.
[NatNum12 D=ordinal]\""hola" \" D MMM => "hola " third Jan

(In reply to m.a.riosv from comment #5)

> Quotes, one more example.
> [NatNum12 D=ordinal]\""hola" \" D MMM => "hola " third Jan

Let's be more specific, to clarify what is not working.

"D MMM" is a **DATE** format > seems to be working.

Now, what about a **NUMBER** format? > it is not working as expected (with a recent LO 24.2 alpha).

Examples:
--------

Cell Value (with decimal point):
1.23

[NatNum12 capitalize EUR]0.00
One euro and twenty-three cents

Format:
[NatNum12 capitalize EUR]\""Total: "\"0.00
Actual result:
"Total: "1.23
Expected result:
"Total: "One euro and twenty-three cents


[NatNum12 capitalize EUR]\"Total: \"0.00
"Total: "1.23

[NatNum12 capitalize EUR]"Total: "0.00
Total: 1.23

[NatNum12 capitalize EUR]Total: 0.00
Total: 1.23


[NatNum12 cardinal]0.00
one point two three

[NatNum12 cardinal]\""Total: "\"0.00
"Total: "1.23

[NatNum12 cardinal]\"Total: \"0.00
"Total: "1.23

[NatNum12 cardinal]"Total: "0.00
Total: 1.23

[NatNum12 cardinal]Total: 0.00
Total: 1.23

Hopefully these examples can be reproduced and are enough to show what seems to not be working as expected (or much more documentation is needed, somewhere).

(In reply to ady from comment #6)
> Format:
> [NatNum12 capitalize EUR]\""Total: "\"0.00
> Actual result:
> "Total: "1.23
> Expected result:
> "Total: "One euro and twenty-three cents

Actually, considering the combination of backslash and quotation marks, I'm not even sure about the precise expected result anymore, but the number is surely not converted, so that's not working.

Error since 6.1

(In reply to gmolleda from comment #8)
> Error since 6.1

The format was introduced in LO 6.1

https://wiki.documentfoundation.org/ReleaseNotes/6.1#Localization

So, either an implementation error, or the possibility is not supported (yet?).

FWIW, there are possible workarounds in terms of presentation, such as (for example, among others):
="Total: "&TEXT(1.23;"[NatNum12 cardinal]0.00")

That workaround needs an auxiliary cell, because the result of this cell (formula) is a text value, not a numeric value presented in text format.

Same behavior in Version: 25.8.3.2 (X86_64)
Build ID: 8ca8d55c161d602844f5428fa4b58097424e324e
CPU threads: 4; OS: Linux 6.11; UI render: default; VCL: gtk3
Locale: es-ES (es_ES.UTF-8); UI: es-ES
Calc: threaded

The Ady's workaround work well. Thanks.