The same as you do in English.
This noun doesn't exist in French. Maybe you would mean "bête"? "Bête" is a beast or an idiot.
"Life is joy" in French is "la vie est joie."
It wouldn't change. It would still be Elisabeth. Actually it would, pronunciation wise it would be Elizzhabett. No french name as Beth i have ever heard of. :-)
Je suis tres heureux
Je m'appelle......is how you say my name is.......in French.
la joie dans le matin
My name is (whatever) is "Mon nom est ..." or "je m'appelle ..." in French.
Same way just with alittle accent
probably "la joie de ma vie"
Beth ydy enw ein ysgol ni? or Beth yw enw ein hysgol ni?
It's not a French name
It's not a French name