"Home is where the cat is."
Translation:Дім там, де кіт.
It would not really be "Home is home only if there is a cat". That would be "Дім — це дім, тільки якщо там є кіт". "Дім там, де є кіт" would translate as "Home is where there is a cat", not "Home is where the cat is".
We omit "є" in two places here: Дім (є) там де (є) кіт. In Ukrainian in general we omit "to be" in present tense.
All platforms have it built-in. Windows, Apple OS & iOS, and Android. Just go into the Language/Keyboard settings and add the Ukrainian keyboard.
On Android, if your keyboard is the standard Gboard, hold down the comma (,) and select the little "⚙️ gear" icon and select "Languages."
In English you can skip the word "there" because it's understood: "Home is (there) where the cat is". In Ukrainian, the word "де" splits this sentence into two (thus the comma), and in principle "де" belongs to the sentence with "кіт". Дім там (1), де кіт (2). The second part "де (є) кіт" has "кіт" as the subject, the hidden "є" as the verb, and "де" connected to the verb "є". If you don't use "там" and simply say "Дім, де кіт" it's just really not enough information in the "Дім" part :)
I have been thinking about it, and if I repeat "Дім де кіт" many times, it sounds OK, kind of, grammatically acceptable. But it does not make much sense semantically because it doesn't have enough information to understand what's happening with "де".
Another example, someone is asking you, "where are you?" and you reply "I'm where you forgot your umbrella yesterday". That would be "Я там, де ти вчора забув парасольку". Saying it without "де": "Я де ти вчора забув парасольку" kind of works in spoken language, but it really sounds kind of broken and incomplete.
Based on my "native speaker gut feeling" I conclude without "там" it doesn't work. But it could be that it's grammatically correct and should be accepted, and the fact that it sounds wrong to me means nothing :D But I don't know where I can find this info :)