SELECT 
  b.*, 
  d.*, 
  c.* 
FROM 
  jmj_bm_blocks as b 
  LEFT JOIN jmj_bm_blocks_descriptions as d ON b.block_id = d.block_id 
  LEFT JOIN jmj_bm_blocks_content as c ON b.block_id = c.block_id 
  AND d.lang_code = c.lang_code 
WHERE 
  b.block_id = 300 
  AND d.lang_code = 'en' 
ORDER BY 
  snapping_id DESC 
LIMIT 
  1

Query time 0.00175

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "2.40"
    },
    "ordering_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "nested_loop": [
        {
          "table": {
            "table_name": "b",
            "access_type": "const",
            "possible_keys": [
              "PRIMARY"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "block_id"
            ],
            "key_length": "4",
            "ref": [
              "const"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 1,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "0.00",
              "eval_cost": "0.20",
              "prefix_cost": "0.00",
              "data_read_per_join": "224"
            },
            "used_columns": [
              "block_id",
              "type",
              "properties",
              "company_id",
              "storefront_id"
            ]
          }
        },
        {
          "table": {
            "table_name": "d",
            "access_type": "const",
            "possible_keys": [
              "PRIMARY"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "block_id",
              "lang_code"
            ],
            "key_length": "10",
            "ref": [
              "const",
              "const"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 1,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "0.00",
              "eval_cost": "0.20",
              "prefix_cost": "0.00",
              "data_read_per_join": "208"
            },
            "used_columns": [
              "block_id",
              "lang_code",
              "name"
            ]
          }
        },
        {
          "table": {
            "table_name": "c",
            "access_type": "ref",
            "possible_keys": [
              "PRIMARY"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "block_id"
            ],
            "key_length": "4",
            "ref": [
              "const"
            ],
            "rows_examined_per_scan": 2,
            "rows_produced_per_join": 2,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "2.00",
              "eval_cost": "0.40",
              "prefix_cost": "2.40",
              "data_read_per_join": "448"
            },
            "used_columns": [
              "snapping_id",
              "object_id",
              "object_type",
              "block_id",
              "lang_code",
              "content"
            ],
            "attached_condition": "<if>(is_not_null_compl(c), (`jmj_test`.`c`.`lang_code` = 'en'), true)"
          }
        }
      ]
    }
  }
}