How would a native speaker react to the proverbial phrase: "Life is lethal"?

Would it sound completely wrong?

Would it be understood humoristically?

Would "deadly" be better?

It's an attempt to translate the humoristic German sentence:

Das Leben ist tödlich.

I often use it as a reply to for example people expressing their fear of statistically unlikely events such as being involved in a plane crash or the like. But can it even be translated to still be kind of funny?

There is no need to ask about a translation, or if it would be appropriate in English, because there are several variations of this proverb already in existence in English, one of which dates all the way back to 1656.

From the Quote Investigator:

Life is a sexually transmitted terminal disease.

Would you please explore its provenance?

Quote Investigator: Tracing this statement is difficult because it emerged from a family of related sayings. Here is a summary snapshot showing quotations with dates:

1656: Life is an Incurable Disease. —Abraham Cowley
1943: Some people think of life as a fatal disease. —Francis T. Cunningham
1968: Life is a hereditary disease. —Anonymous Graffito
1971: Life is a terminal disease. —Anonymous Graffito
1980: Life is a sexually transmitted disease. —Anonymous Graffito
1981: Life is just another sexually transmitted social disease. —Margaret Atwood
1982: Life is a sexually transmitted disease. — attributed to Posy Simmonds
1982: Life is a sexually transmitted disease. —Guy Bellamy
1984: Life is a sexually transmitted terminal disease. —Marilyn Duckworth
1985: Life is a sexually transmitted disease & there’s a 100% mortality rate. —R. D. Laing

In 1997, Paula Gunn Allen published "Life Is a Fatal Disease: Selected Poems, 1962-1995."

In 2004, Lis Harvey released the song "Life Is Fatal."

In 2009, Zeke Hoskin released the song "Life Is Lethal."

So, this saying, and its variations, have been part of English culture for a while now.