SELECT 
  v.variant_id, 
  v.product_id, 
  vd.variant, 
  vf.position, 
  vf.color 
FROM 
  cscart_product_features_values v 
  LEFT JOIN cscart_product_feature_variant_descriptions vd ON v.variant_id = vd.variant_id 
  AND vd.lang_code = 'en' 
  LEFT JOIN cscart_product_feature_variants vf ON v.variant_id = vf.variant_id 
WHERE 
  1 
  AND v.feature_id = 345 
  AND v.product_id IN (
    '18899', '39128', '39129', '39130', 
    '39131', '39132', '39133', '39134', 
    '39135', '39136', '39137', '39138', 
    '39139', '39140', '39141', '39142', 
    '39143', '39144', '39145', '39146'
  )

Query time 0.00133

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "18.45"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "v",
          "access_type": "range",
          "possible_keys": [
            "PRIMARY",
            "fl",
            "product_id",
            "fpl",
            "idx_product_feature_variant_id"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "feature_id",
            "product_id"
          ],
          "key_length": "6",
          "rows_examined_per_scan": 20,
          "rows_produced_per_join": 20,
          "filtered": "100.00",
          "using_index": true,
          "cost_info": {
            "read_cost": "2.45",
            "eval_cost": "2.00",
            "prefix_cost": "4.45",
            "data_read_per_join": "15K"
          },
          "used_columns": [
            "feature_id",
            "product_id",
            "variant_id"
          ],
          "attached_condition": "((`chocoramo`.`v`.`feature_id` = 345) and (`chocoramo`.`v`.`product_id` in ('18899','39128','39129','39130','39131','39132','39133','39134','39135','39136','39137','39138','39139','39140','39141','39142','39143','39144','39145','39146')))"
        }
      },
      {
        "table": {
          "table_name": "vd",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "variant_id",
            "lang_code"
          ],
          "key_length": "9",
          "ref": [
            "chocoramo.v.variant_id",
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 20,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "5.00",
            "eval_cost": "2.00",
            "prefix_cost": "11.45",
            "data_read_per_join": "60K"
          },
          "used_columns": [
            "variant_id",
            "variant",
            "lang_code"
          ]
        }
      },
      {
        "table": {
          "table_name": "vf",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "variant_id"
          ],
          "key_length": "3",
          "ref": [
            "chocoramo.v.variant_id"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 20,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "5.00",
            "eval_cost": "2.00",
            "prefix_cost": "18.45",
            "data_read_per_join": "22K"
          },
          "used_columns": [
            "variant_id",
            "color",
            "position"
          ]
        }
      }
    ]
  }
}