SELECT 
  a.*, 
  b.* 
FROM 
  cscart_ecl_meta_tags_patterns AS a 
  INNER JOIN cscart_ecl_meta_tags_patterns_descriptions AS b ON (
    b.pattern_id = a.pattern_id 
    AND b.lang_code = 'ru'
  ) 
WHERE 
  a.company_id = 1 
  AND a.pattern_id = 9

Query time 0.00305

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "a",
      "access_type": "const",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "3",
      "used_key_parts": ["pattern_id"],
      "ref": ["const"],
      "rows": 1,
      "filtered": 100
    },
    "table": {
      "table_name": "b",
      "access_type": "const",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "9",
      "used_key_parts": ["pattern_id", "lang_code"],
      "ref": ["const", "const"],
      "rows": 1,
      "filtered": 100
    }
  }
}