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

Query time 0.00020

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.004417794,
    "nested_loop": [
      {
        "table": {
          "table_name": "lang",
          "access_type": "range",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "392",
          "used_key_parts": ["lang_code", "name"],
          "loops": 1,
          "rows": 2,
          "cost": 0.004417794,
          "filtered": 100,
          "index_condition": "lang.lang_code = 'en' and lang.`name` in ('sign_in_to_buy','text_login_to_add_to_cart','text_login_to_add_to_cart','sign_in_to_buy','text_login_to_add_to_cart','text_login_to_add_to_cart')"
        }
      }
    ]
  }
}