SELECT 
  b.variant_name, 
  a.*, 
  IF(
    shared_option_variants.variant_id IS NOT NULL, 
    shared_option_variants.modifier, 
    a.modifier
  ) as modifier, 
  IF(
    shared_option_variants.variant_id IS NOT NULL, 
    shared_option_variants.modifier_type, 
    a.modifier_type
  ) as modifier_type 
FROM 
  cscart_product_option_variants AS a 
  LEFT JOIN cscart_product_option_variants_descriptions AS b ON b.variant_id = a.variant_id 
  AND b.lang_code = 'ja' 
  LEFT JOIN cscart_ult_product_option_variants shared_option_variants ON shared_option_variants.variant_id = a.variant_id 
  AND shared_option_variants.company_id = 1 
WHERE 
  1 
  AND a.option_id IN (84) 
  AND a.status = 'A' 
ORDER BY 
  a.position, 
  a.variant_id

Query time 0.00243

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "shared_option_variants",
      "access_type": "system",
      "possible_keys": ["PRIMARY", "company_id"],
      "rows": 0,
      "filtered": 0,
      "const_row_not_found": true
    },
    "read_sorted_file": {
      "filesort": {
        "sort_key": "a.position, a.variant_id",
        "table": {
          "table_name": "a",
          "access_type": "ref",
          "possible_keys": ["status", "option_id", "option_id_2"],
          "key": "option_id",
          "key_length": "6",
          "used_key_parts": ["option_id", "status"],
          "ref": ["const", "const"],
          "rows": 2,
          "filtered": 100,
          "index_condition": "a.`status` = 'A'",
          "attached_condition": "a.option_id <=> 84 and a.`status` <=> 'A'"
        }
      }
    },
    "table": {
      "table_name": "b",
      "access_type": "eq_ref",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "9",
      "used_key_parts": ["variant_id", "lang_code"],
      "ref": ["markins_test.a.variant_id", "const"],
      "rows": 1,
      "filtered": 100,
      "attached_condition": "trigcond(b.lang_code = 'ja')"
    }
  }
}