If the store supports multiple languages, you can translate display text per language. Where you translate depends on the type of text.
Set these on the "Translate" screen of each selling period rule. The targets are as follows.
Product messages (before, during, and after the selling period)
Alert messages (before and after the selling period)
Countdown timer title and description
For a language without a translation, the original text in the rule is shown. You can choose languages added in Shopify, except the default language.
Countdown timer units (days, hours, minutes, and seconds) are not translated in the rule. In Shopify Translate & Adapt, go to Theme → Templates → Product, then translate "Countdown Timer."