SELECT 
  feature_id, 
  variant_id, 
  value, 
  value_int 
FROM 
  cscart_product_features_values 
WHERE 
  product_id = 10012 
  AND lang_code = 'en'

Query time 0.00039

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 64 Using where

Result

feature_id variant_id value value_int
127 5895
128 5899
129 5903
30 128
42 6256
24 108
135 5968
136 5973
135 5965
136 5972
136 5977
176 6262
178 6306
136 5976
176 6260
176 6270
176 6271