SELECT 
  lang.name, 
  lang.value 
FROM 
  cscart_language_values lang 
WHERE 
  lang.lang_code = 'en' 
  AND lang.name IN (
    'sign_in', 'proceed_to_checkout', 
    'proceed_to_checkout', 'sign_in', 
    'proceed_to_checkout', 'proceed_to_checkout'
  )

Query time 0.00044

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "2.81"
    },
    "table": {
      "table_name": "lang",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "lang_code",
        "name"
      ],
      "key_length": "392",
      "rows_examined_per_scan": 2,
      "rows_produced_per_join": 2,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "2.41",
        "eval_cost": "0.40",
        "prefix_cost": "2.81",
        "data_read_per_join": "816"
      },
      "used_columns": [
        "lang_code",
        "name",
        "value"
      ],
      "attached_condition": "((`webmarco`.`lang`.`lang_code` = 'en') and (`webmarco`.`lang`.`name` in ('sign_in','proceed_to_checkout','proceed_to_checkout','sign_in','proceed_to_checkout','proceed_to_checkout')))"
    }
  }
}