"It is raining at night."
Translation:Il pleut la nuit.
The English translation is a bit weird though.
This is one of the cases in English that present simple tense and present continuous tense don't mean the same thing.
Present simple tense " It rains at night / the night " means it is a habitual thing that it usually rains at night.
Present continuous tense " It is raining at night / the night " does not mean the same.
Present simple tense and present continuous tense are NOT 100% interchangeable in English.