SELECT 
  pfv.feature_id, 
  pfv.product_id, 
  pfv.variant_id, 
  gp.group_id 
FROM 
  cscart_product_features_values AS pfv 
  INNER JOIN cscart_product_variation_group_products AS gp ON pfv.product_id = gp.product_id 
  INNER JOIN cscart_product_variation_group_features AS gpf ON gpf.group_id = gp.group_id 
  AND gpf.feature_id = pfv.feature_id 
WHERE 
  pfv.lang_code = 'ru' 
  AND gp.group_id IN (200, 201, 203)

Query time 0.00053

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "10.51"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "gpf",
          "access_type": "range",
          "possible_keys": [
            "PRIMARY",
            "idx_group_id"
          ],
          "key": "idx_group_id",
          "used_key_parts": [
            "group_id"
          ],
          "key_length": "3",
          "rows_examined_per_scan": 3,
          "rows_produced_per_join": 3,
          "filtered": "100.00",
          "index_condition": "(`test_uchur_k`.`gpf`.`group_id` in (200,201,203))",
          "cost_info": {
            "read_cost": "1.81",
            "eval_cost": "0.30",
            "prefix_cost": "2.11",
            "data_read_per_join": "312"
          },
          "used_columns": [
            "feature_id",
            "group_id"
          ]
        }
      },
      {
        "table": {
          "table_name": "gp",
          "access_type": "ref",
          "possible_keys": [
            "PRIMARY",
            "idx_group_id"
          ],
          "key": "idx_group_id",
          "used_key_parts": [
            "group_id"
          ],
          "key_length": "3",
          "ref": [
            "test_uchur_k.gpf.group_id"
          ],
          "rows_examined_per_scan": 4,
          "rows_produced_per_join": 12,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "3.00",
            "eval_cost": "1.20",
            "prefix_cost": "6.31",
            "data_read_per_join": "192"
          },
          "used_columns": [
            "product_id",
            "group_id"
          ]
        }
      },
      {
        "table": {
          "table_name": "pfv",
          "access_type": "ref",
          "possible_keys": [
            "PRIMARY",
            "fl",
            "lang_code",
            "product_id",
            "fpl",
            "idx_product_feature_variant_id"
          ],
          "key": "fpl",
          "used_key_parts": [
            "feature_id",
            "product_id",
            "lang_code"
          ],
          "key_length": "12",
          "ref": [
            "test_uchur_k.gpf.feature_id",
            "test_uchur_k.gp.product_id",
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 12,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "3.00",
            "eval_cost": "1.20",
            "prefix_cost": "10.51",
            "data_read_per_join": "9K"
          },
          "used_columns": [
            "feature_id",
            "product_id",
            "variant_id",
            "lang_code"
          ]
        }
      }
    ]
  }
}

Result

feature_id product_id variant_id group_id
193 51329 1361 200
193 51328 1360 200
193 51327 1359 200
193 50985 1358 200
193 51331 1360 201
193 51330 1359 201
193 50986 1358 201
193 51332 1361 201
193 51339 1361 203
193 51338 1360 203
193 51337 1359 203
193 51336 1358 203
193 50988 1357 203