SELECT 
  feature_id, 
  variant_id, 
  value, 
  value_int 
FROM 
  cscart_product_features_values 
WHERE 
  product_id = 725 
  AND lang_code = 'en'

Query time 0.00038

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 56 Using where

Result

feature_id variant_id value value_int
127 5895
128 5899
136 5976
176 6270
135 5968
178 6306
42 149
24 109
129 5903
30 128
176 6262
176 6260
135 5967
135 5964
136 5972