I've never heard of a glass (a drinking glass) described as weak. Delicate or fragile, maybe. What does the word gyenge mean in this context (in Hungarian)? Would the speaker really be saying that the glass is weak? I don't think that's the best English word for the translation.
It seems that they have changed the English translation without changing the Hungarian word. The English now says "fragile" but the Hungarian still say "gyenge" (which means weak) rather than "törékeny" (which means fragile as others have pointed out here).
Unfortunately, I think this means that the sentence still sounds weird to Hungarians and the English speakers are learning the wrong meaning for gyenge. :(
My mother (native Hungarian speaker) says: "Ez egy gyenge pohár" translates as "This is not quite a full cup" (of X), as in a cookbook recipe. E.g.; "Add not quite a full cup" = gyenge pohár. As others have stated before, if the meaning desired is (fragile, breakable), then törékeny is appropriate.
There are several different possibilities
|a glass for drinking water (or wine)||glass||pohár|
|a plastic cup for drinking water (or playing beer pong)||cup||pohár|
|a fancy cup (for drinking tea/coffee)||cup||csésze|
|a mug (for drinking tea/coffee)||mug||bögre|
|a bottle, made of glass (a bottle of wine)||bottle||üveg|
|a bottle, made of plastic (a bottle of water)||bottle||palack|
|glass as a material||glass||üveg|