Fount solution ti place there just one character colon, which not generates <p></p> on final translated page.

I was able to create an empty translation unit using the normal editor (“Show in wiki editor” in the dropdown opened by clicking the message name), and it went through (i.e. the translation page was edited to remove the English text without adding anything instead of it), so it’s only Tux that prevents it. By the way, the ability to create blank pages was requested in T59238 exactly to allow blanking translations.

Thanks @Tacsipacsi that's true, it is possible by this way. But for UX it is not comfortable and also require turned on qqq for describe, why it's empty.

In T309684#8482058, @JacksonsonSK wrote:

But for UX it is not comfortable

I agree, Tux (the Special:Translate interface) should be changed not to prevent it (but it should still require some sort of confirmation to avoid accidental blanking).

and also require turned on qqq for describe, why it's empty.

Why? qqq is to describe things that apply to all translations. The reason for blanking one particular translation should be in the edit summary (which is now shown in the right column).

Indeed. I forgot that!
Anyway, it will be maybe useful to add parameter to translate which content
will be showed before qqq or in installations without qqq.
For example: <translate desc="Currency code">€</translate> this will be
more easy like over qqq

If you think there should be a way to add message documentation through the source page text, please create a new task for that. (I don’t think it’s worth making source text more complicated.) Let’s keep this task focused on allowing to create blank translations.