Modern Hebrew uses Sephardic pronunciation, not that of these European Jews, so "Shabbat" not "Shabbes"
So 
in Kiryas Yoel gut shabbes is the right call, whereas in other areas... [DOC] [TLE] Ashkenazim and the Sephardic Pronunciation of Hebrew [PAR] Jan 8, 2010 ... Those who study Hebrew these days may learn both pronunciations, yet ...