IN CASE OF DIFFICULTIES WITH FRENCH LANGUAGE? PLEASE AIM TO LAND OR TAKE OFF BEFORE 11.30 UTC OR AFTER 13.00 UTC.
That is not necessary.
Conversation in French is
not required. Making the standard calls using French terminology is obviously helpful and is what is intended by the remark: "make circuit calls in French when ATC is not available". This is a relaxation of the French Rules of the Air but it is not an instruction to speak French.
The Le Touquet airport website provides a link to an excellent site, for non French speakers, that explains all this in detail and should put minds at rest;
'Idiot -proof French Radio Procedures' which is provided by Lingaero.com.
The UK GAR form is a 'General Declaration' for UK purposes.