SELECT 
  category_id, 
  category 
FROM 
  cscart_category_descriptions 
WHERE 
  category_id IN (501, 502, 503) 
  AND lang_code = 'de'

Query time 0.00131

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_category_descriptions range PRIMARY PRIMARY 9 3 Using index condition

Result

category_id category
501 Dekoration
502 Verblender
503 Steinriemchen Innen