That code would only guess wrong if all of the following are true:
- The text is encoded using Windows-1252 (or iso-8859-1),
- At least one of [€‚ƒ„…†‡ˆ‰Š‹ŒŽ‘’“”•–—˜™š›œžŸ<NBSP>¡¢£¤¥¦§¨©ª«¬<SHY>®¯°±²³´µ¶·¸¹º»¼½¾¿ÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷] is present,
- All instances of [ÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞß] are always followed by exactly one of [€‚ƒ„…†‡ˆ‰Š‹ŒŽ‘’“”•–—˜™š›œžŸ<NBSP>¡¢£¤¥¦§¨©ª«¬<SHY>®¯°±²³´µ¶·¸¹º»¼½¾¿],
- All instances of [àáâãäåæçèéêëìíîï] are always followed by exactly two of [€‚ƒ„…†‡ˆ‰Š‹ŒŽ‘’“”•–—˜™š›œžŸ<NBSP>¡¢£¤¥¦§¨©ª«¬<SHY>®¯°±²³´µ¶·¸¹º»¼½¾¿],
- All instances of [ðñòóôõö÷] are always followed by exactly three of [€‚ƒ„…†‡ˆ‰Š‹ŒŽ‘’“”•–—˜™š›œžŸ<NBSP>¡¢£¤¥¦§¨©ª«¬<SHY>®¯°±²³´µ¶·¸¹º»¼½¾¿],
- None of [øùúûüýþÿ] are present, and
- None of [€‚ƒ„…†‡ˆ‰Š‹ŒŽ‘’“”•–—˜™š›œžŸ<NBSP>¡¢£¤¥¦§¨©ª«¬<SHY>®¯°±²³´µ¶·¸¹º»¼½¾¿] are present except where previously mentioned.
In other words, that code is very reliable.