Agree, but that is impossible with "raw native SQL" at the moment as there is no such "raw native" in-build function in SQL.

Lets call MS to extend their FORMAT function in SQL2012...

Again, it'd depend what you call by "portability". I'm sure if you would need to port your system to different English, you would need to convert your words again.

Let say 1,000,000,000:

In short scale (American English) it's called billion (widely used in finance and other fields), but in Long Scale (many European languages) it's called as milliard or just thousand million. As traditionally the billion is used for one million, million (1,000,000,000,000), which is called as trillion in US (short scale).

There are plenty more differences in wording of numbers eg. using "AND" between some fractions...

So, I cannot see how you can achieve good portability by saving it in database. I would think the FORMAT based on locale would be the best choice.