SELECT 
  feature_id, 
  variant_id, 
  value, 
  value_int 
FROM 
  cscart_product_features_values 
WHERE 
  product_id = 402 
  AND lang_code = 'de'

Query time 0.00040

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_product_features_values ref lang_code,product_id,product_id_idx,product_feature_idx product_id 3 const 55 Using where

Result

feature_id variant_id value value_int
135 5967
135 5963
42 6251
30 128
127 5895
128 5899
129 5903
176 6260
24 107
135 5968
136 5973
176 6271
178 6306
176 6262
176 6270