Bug #81281 implemented the [nbsp] representation for non-breaking spaces.
In French typography, narrow non-breaking spaces are needed before ";!?" chars (perhaps also before ":»" and after "«", this is not clear for these).
I found this is also used at least in Mongolian and in Persian.
This char (U+202F) is not supported every where yet (but no problem with good unicode fonts as found in Ubuntu default install for example). The best would be to have an automatic fall-back on nbsp (U+00A0) when U+202F is unsupported, but this is not a Launchpad issue.
So here we need a "[nnbsp]" tag which correspond to \u202F
"[nnbsp]" is a bit odd, a localised version may be better (eg "[fine]" in French), but I don't know if this fit Launchpad policy...