Original discussion in http://lists.gnucash.org/pipermail/gnucash-devel/2011-August/032481.html

A bit of background: in Austria where I live, most companies use an account
hierarchy scheme which is hierarchically numbered, typically in 4-digit numbers. The numbering scheme is nationally standardized. I know a similar system exists in Germany, albeit with a set of industry specific account hierarchies (some of them available as GnuCash account hierarchy templates). I'm not sure about other European countries.

Now, while GnuCash does allow for accounts to be assigned a number,
those numbers are not available to actually be selected in the
register when making an entry. That complicates matters for users
using a numbered accounting scheme -- specifically because, as the
account number identifies the account unequivocally, the account
hierarchy scheme does not enforce uniqueness among leaf account
names. In GnuCash, this problem can be worked around by referring to
accounts by their full name (as opposed to just the leaf account
names) -- but that's comparatively tedious, compared to identifying an
account by its number.

Some existing account hierarchies (in the de_DE locale) presently work
around this limitation rather crudely, by including the account number
as a prefix to the account name. Apart from that being a rather
inelegant redundancy, it also creates a suboptimal user experience:
GnuCash displays account names right-aligned in the register -- so for
long account names, even if the "only display leaf account names"
option is checked, the account number is often invisible.

Thus, my suggestion is to add an option to display account codes in
the register and account selection dialog. Then, if said option is
checked, the account selection dropdown would display account numbers
and enable users to quickly select an account by typing 3-4 numeric
keys.

Going down the rabbit hole, it would of course make sense to
optionally include the account numbers in reports too -- but I believe
this is safe to defer until after the basic functionality exists