A libnah is a traditional land area measurement used, as far as I know, only in Yemen. It has no equivalent term in English, so I would say use the transliteration and explain it, especially since it is much smaller than an acre or a hectare.
Even in Yemen the size of a libnah varies from one city to another. In Sana'a, a libnah is 44.44 sq. m. while other regions could be larger or smaller. For example, in 'Amran north of Sana'a, a libnah is 64 sq. m.

The libnah or lubnah is an areal measure used widely on the high plateaux and in
the mountains of the northern part of the Yemen. It varies widely in size