SELECT 
  feature_id, 
  variant_id, 
  value, 
  value_int 
FROM 
  cscart_product_features_values 
WHERE 
  product_id = 526 
  AND lang_code = 'de'

Query time 0.00093

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_feature_idx 3 const 74 Using where

Result

feature_id variant_id value value_int
19 92 0.800
20 6058 1.100
21 96
22 99
23 6273
24 107
30 6131
42 145
127 5895
128 5899
129 5902
134 6238
152 6095
152 6094
152 6105
152 6092
152 6089
152 6088
152 6096
178 6317