From my MA Dissertation:
Inculturation is centred on culture. This marks the primary difference between inculturation and contextualisation. Most Protestants consider inculturation as a subset of contextualisation. Bosch for example, placed inculturation under contextualisation together with liberation theology; with inculturation the primary concern is the relationship between faith and culture, while liberation theology includes the larger context, namely the socio-political situation. So although there remains close ties between culture and the socio-political context, when inculturation is in question, the focus should always be ‘culture’.
 Bosch, Transforming Mission: Paradigm Shifts in Theology of Mission (American Society of Missiology Series) 1991, 420ff.
By the way, a new edition of David Bosch’s masterpiece has been published:
Bosch, Transforming Mission: Paradigm Shifts in Theology of Mission (20th Anniversary Edition) (American Society of Missiology)