That difference between the literal word-by-word translation [1] and the semantic translation is my point of focus.
In English, my suggested translation would be that “It isn’t worth it.” But since this word-for-word translation would feel unnatural (that is, it’s typically better to introduce « la peine » even if the word trouble/pain wasn’t in the original sentence), there can be an extra cognitive load that interrupts fluency.
With enough conscious practice to train this, the translation of common idioms can become automatic. But meaningful translation instead of literal translation of idioms (especially of those more rarely used) can be a potential reason for someone to stop thinking in a target language, and revert to one’s native language to start thinking of the most natural translation for the phrase.
As another example, if I want to say “When pigs fly” in French, my instinct is to stop and use another phrase because the word-by-word translation is probably unnatural. In this case, my instinct is correct, as the proper meaningful translation is « Quand les poules ont les dents » (word-by-word translation: ‘When chicken have teeth’). So, dealing with idiom translation is an added mental effort to translate, which may cause thinking in one’s native language for some people.
The variations of the idiom's translations are definitely interesting. If you're curious to read more about the language variations, Le Figaro has a nice article about the idiom's equivalent in other languages (though they use the variant « quand les poules auront les dents »).
From Le Figaro [1]: « Précisons enfin que notre expression est un idiotisme et qu'elle ne possède pas, par conséquent, de stricts équivalents à l'étranger. Ainsi nos voisins anglais ont-ils l'habitude de dire «quand les cochons voleront», les Espagnols, de lancer «quand les grenouilles auront des poils» et les Allemands, de flanquer un «quand les poissons apprendront à voler». »
English translation: "Finally, let us specify that our expression is an idiom and that it does not, therefore, have strict equivalents abroad. Thus our English neighbors are used to saying "when the pigs fly", the Spaniards say "when the frogs have hair" and the Germans say "when the fish learn to fly."
Thanks; I didn't know "idiom" is "idiotisme". Nice.
The examples from Figaro all seem to have their verb as a subjunctive in French, so "When pigs would fly" - we usually say "If pigs had wings", or "Yeah, and pigs might fly". Your translations don't carry the doubt that words like "might" and "if" impart. There are hardly any/no verbs in English that still have a subjunctive distinct from the indicative, a fact that I regret.
There are some places in England (north east) where they pronounce the subjunctive of "to be", even though it isn't written distinctly; they say "If I wear a rich man". I think it's from the German, as in "Wenn ich wäre".
"Peine" isn't just pain; it's also trouble. So I think "It's not worth the trouble" is a better rendition.
/me a native English speaker, who learned French by immersion aged about 6.