internal/number: added per-language format patterns Change-Id: I79ef2b032565b6807c658fe6bb641a95a6e4cb9c Reviewed-on: https://go-review.googlesource.com/25133 Reviewed-by: Nigel Tao <nigeltao@golang.org> Run-TryBot: Marcel van Lohuizen <mpvl@golang.org>