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

Query time 0.00116

JSON explain

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