"Your tea's getting cold" generally tends to me "Your dinner is getting cold" in British English.
Also, for those who are confused, it's good to note that "worden" is the same as "becoming", and in English, we use "get" as a replacement for "become".
"It's getting cold" = "It's becoming cold"
Why don't they suggest "to get" as a possible translation? I'm always afraid of using English "too naturally" when translating, just in case I might change the meaning, so I tend to use only the words Duoling suggests me to use. "To get" should be added, as it sounds pretty good :)