SELECT 
  search_phrases 
FROM 
  cscart_ab__search_motivation 
WHERE 
  category_id = 879 
  AND lang_code = 'ru'

Query time 0.00026

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_ab__search_motivation",
      "access_type": "ref",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "3",
      "used_key_parts": ["category_id"],
      "ref": ["const"],
      "rows": 1,
      "filtered": 100,
      "attached_condition": "cscart_ab__search_motivation.lang_code = 'ru'"
    }
  }
}