UTF8 export problem

Export with PDF : did it work better before V5.1 ?

Export to Excel : there is no export to Excel. Export is to CSV.
Could you try and open exported file (CSV) with text editor such as Notedpad++. It should b e correct.
I'm afraid Excel does not correctly import UTF-8 non ansi characters.
Maybe some conversion may be required before.

You're right.
utf8_decode was used to correctly display accentuated characters in Excel.
But this is valid only for western europe charsets.
Ticket #1870 recorded to try and parameter whever utf8_decode must be used on CSV export.

But the problem for PDF files already exists and I cannot follow the problem, so please advise.

This is a real problem, as non ansi characters are not correctly exported in pdf format.
If may be due to font used.
Ticket #1871 recorded to investigate.
NB : as a workaround, you can use a pdf printer, such as PDF Creator to generate PDF form printable report.

I suggest that you consider enabling enforceUtf8 by default for the next version, since it is more common.

It is, but only for new installs. It is not for existing installs as it will generate issues if MySql server in not cerrectly configured as UTF8.