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.
Weak, structurally weak, weak in material, easily breakable. You just touch it and it breaks.
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. :(
Hungarians never say "weak glass". Yeah, "fragile" is the correct word (törékeny). Or you can say "thin" what is not a proper translation, but means the same if you speak about glasses.
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.