I made some research and found out that words like
いただきます
こちそうさまでした
よろしくお願いします
Are not really translatable.
I also find it difficult to translate Japanese generally to another language since things are said in a different way in Japanese sometimes, propably because of the unique grammar and words like せっかく and also because it's so contextual! Interesting, isn't it?
My own point of view is that there is no such thing as an untranslatable word. When someone says something is untranslatable, what they mean is that they don’t know how to translate it.
I wouldn't say that カッコ可愛い is hard to translate but it's moreso the fact that it's hard to translate a word that's a combination of two words. The only thing I could come up with is "awwwsome". When translating japanese, you can't really stick to dictionary definitions and have to use some creative liberties. For example, うっせー and うるさい are both used as a way to say shut up, but to me, I think it's better to translate them differently: うるさい - "shut up" / うっせー - "shut up already!". I think words that are "untranslatable" are actually more fun to translate
