SELECT 
  feature_id, 
  variant_id, 
  value, 
  value_int 
FROM 
  cscart_product_features_values 
WHERE 
  product_id = 10139 
  AND lang_code = 'de'

Query time 0.00043

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
127 5895
128 5899
129 5902
42 146
22 98
21 95
24 107
75 243
30 240
149 0 5702327224637
20 6052 1.300
178 6308
23 6297
19 106 1.000
134 5961