Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
sluggish [ˈslʌgɪʃ] adj (stream) ме́дленно теку́щий#; (engine) пло́хо рабо́тающий; (person) медли́тельный*медли́телен (trading) вя́лый
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.
Русский: