Should (could) the locale be a document property?

I’m interested in using different locales (specifically, decimal separators and thousands grouping) for different documents.

Correct me if I’m wrong:
Currently (4.1) in Calc the locale is a global installation-wide setting. Let’s assume I have a English global locale (so that 1/3 => 0.3333) and I wish to use a Spanish locale for a single document (so that 1/3 => 0,3333).
The standard recipe (and, it seems, the only way) is to apply a specific number format to some cells (eventually the whole sheet).
If don’t consider this very satisfactory, for several reasons.

For one thing, this only applies to the “formatting”, which is a different concept. The confusion of concepts shows in strange behaviours: the format is used for input/output, but not for the formulas. Assume the scenario above, using English local I’ve formatted all the cells to use Spanish locale.
If I type (without quotes) “=1/4+1” I see 1,25 (that’s ok), if I type “1,25” it is rightly interpreted as the same as 1/4, all right.
But if I type “=0,25+1” or “=1,25” I get an error, th formula expects the literal number in the global locale: “=0.25+1”
Or, if I want to use a function “=MAX(0,25;A1)” , again, is wrong, the number is expected in the global locale, and, further, the formula wants the comma as argument separator (so it couldn’t accept literal numbers with comma separators, of course).

The last issue makes more evident that this recipe: “format all the cells with a different locale” is not what I want. I want a different locale for the document, so that it really overrides the global one.
Ideally, this would allow to work, in the same machine with same LO installation, with simultaneously in two opened Calc documents with different locales.

I don’t know about LO internals, perhaps I’m expecting too much, is this too difficult to implement?

I don’t know if I understand well your question, but you should define the “locale” used in a cell by defining the language of this cell and the number format. If the contents of the cell is recognized in English the decimal separator will be a dot and if it is Spanish, the decimal separator will be a comma.
Of course you can also modify the default style to define the locale for this file. You need to modify the language in the tabs Number and Font.