Looks like you originally had a UTF-8 file which has been interpreted as an 8 bit encoding (e.g. ISO-8859-15) and entity-encoded. I say this because the sequence C3A9 looks like a pretty plausible UTF-8 encoding sequence.
You will need to first entity-decode it, then you'll have a UTF-8 encoding again. You could then use something like iconv to convert to an encoding of your choosing.
To work through your example:
- Ã © would be decoded as the byte sequence 0xC3A9
- 0xC3A9 = 11000011 10101001 in binary
- the leading 110 in the first octet tells us this could be interpreted as a UTF-8 two byte sequence. As the second octet starts with 10, we're looking at something we can interpret as UTF-8. To do that, we take the last 5 bits of the first octet, and the last 6 bits of the second octet...
- So, interpreted as UTF8 it's 00011101001 = E9 = é (LATIN SMALL LETTER E WITH ACUTE)
You mention wanting to handle this with PHP, something like this might do it for you:
//to load from a file, use
//$file=file_get_contents("/path/to/filename.txt");
//example below uses a literal string to demonstrate technique...
$file="&Précédent is a French word";
$utf8=html_entity_decode($file);
$iso8859=utf8_decode($utf8);
//$utf8 contains "Précédent is a French word" in UTF-8
//$iso8859 contains "Précédent is a French word" in ISO-8859
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