SELECT 
  feature_id, 
  variant_id, 
  value, 
  value_int 
FROM 
  cscart_product_features_values 
WHERE 
  product_id = 10011 
  AND lang_code = 'de'

Query time 0.00037

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 43 Using where

Result

feature_id variant_id value value_int
127 5895
128 5899
135 5968
135 5965
136 5976
30 128
42 6256
136 5977
136 5972
136 5973
178 6306
176 6260