SELECT 
  cscart_category_descriptions.category 
FROM 
  cscart_category_descriptions 
  LEFT JOIN cscart_products_categories ON cscart_products_categories.category_id = cscart_category_descriptions.category_id 
WHERE 
  cscart_category_descriptions.lang_code = 'en' 
  AND cscart_products_categories.product_id = 375 
  AND cscart_products_categories.link_type = 'M'

Query time 0.00044

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_products_categories",
      "access_type": "ref",
      "possible_keys": ["PRIMARY", "link_type", "pt"],
      "key": "pt",
      "key_length": "6",
      "used_key_parts": ["product_id", "link_type"],
      "ref": ["const", "const"],
      "rows": 1,
      "filtered": 100,
      "index_condition": "cscart_products_categories.link_type = 'M'"
    },
    "table": {
      "table_name": "cscart_category_descriptions",
      "access_type": "eq_ref",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "9",
      "used_key_parts": ["category_id", "lang_code"],
      "ref": [
        "herbaria_cscart_4_18.cscart_products_categories.category_id",
        "const"
      ],
      "rows": 1,
      "filtered": 100,
      "index_condition": "cscart_category_descriptions.lang_code = 'en'"
    }
  }
}