I have had a look at "newly" published Paris GTFS data which seems very good.
However I was wondering if they use a non EPSG:4326 coordinate system or simply have an error in their output data?
The stops.txt look like: (see attachment)
stop_id,stop_code,stop_name,stop_desc,stop_lat,stop_lon,location_type,parent_station
4025438,,PONT DE NEUILLY - RIVE GAUCHE,,0.8532020217448393,0.0393479059605182,0,452832
4025439,,ALSACE,,0.8532639153293209,0.0392562301471691,0,8419
4025472,,GARE DE LYON - VAN GOGH,,0.8524587493261180,0.0414118995944202,0,439315
4025434,,LES GRAVIERS,,0.8531384698850659,0.0395542054222439,0,8296
4025435,,LES GRAVIERS,,0.8531301551998345,0.0395523141836901,0,8296
I cannot seem to find any EPSG system that would position this coordinate within Paris.