if you cannot see option to translate:
select for example "phpshop product category" from mambelfish's drop down list. (on mbf tranlation page)
If you see nothing, (no categories), then check your table 'mos_pshop_category': is category_id int or varchar?
If it is varchar, then (sorry to say) you have to convert it. Soeren made a little script for it. (It is available in this topic, earlier.)