That view only makes sense if you view translation as purely an encoding process: "let's express in language B exactly the same meaning as in language A". Then sure, you can always do it (as far as I know) if you are willing to accept an unbounded encoding length. Even in a language from an isolated tribe who has never seen a train, you could painstakingly describe all the details of a plain.

However, that seems to me like an over-reductionistic view of translation. Typically, in all except highly technical contexts, you don't only want to convey meaning, you want to keep at least a modicum of naturalness, the feeling that your translated sentence is something that a native speaker of language B might really say.

With that in view, I think it makes sense to say that there are words that are untranslatable in practice. Meaning is not lost, naturalness is.

For example, to say "facepalm" in Spanish you would have to say something like "I place my hand on my face in frustration". Does that convey the meaning? Sure. Has any Spanish speaker ever said it? I highly doubt it, except for the joke of trying to translate something that just doesn't lend itself to it.